Industrial Organic Pigments E-Book

Klaus Hunger

• Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1305

Veröffentlichungsjahr: 2019

Beschreibung

Revised and updated, this highly acclaimed work, now in its fourth edition, remains the most comprehensive source of information available on organic pigments. It provides up-to-date information on synthesis, reaction mechanism, physical and chemical properties, test methods, and applications of all the industrially produced organic pigments available on the world market.

This fourth edition now includes new chapters on the latest applications and three-dimensional X-ray analysis, while the chapters on legislation, ecology, and toxicology have been rewritten to reflect recent developments.

• Sets the international standard for information on the synthesis, reaction mechanisms, properties, relevant test methods, and applications of organic pigments
• Contains all industrially produced pigments of the world market, even those which can no longer be found in producers’ catalogs are described
• Standardized methods allow test results to be compared throughout the book
• The reader is given useful hints as to which pigment is best for a given application
• Clearly structured and concise text with up-to-date references to the pertinent literature
• Ecological and toxicological properties of organic pigments are outlined
• Appendix offers invaluable flow diagrams on the manufacture of numerous pigments, a table of all described pigments with information about their C.I. and CAS registration, and an in-depth subject index

Leseprobe

CONTENTS

Cover

Title Page

Copyright

List of Contributors

Preface to the Fourth Edition

Preface to the Third Edition

Preface to the Second Edition

Preface to the First Edition

List of Abbreviations

Chapter 1: General

1.1 Definition: Pigments and Dyes

1.2 Historical

1.3 Classification of Organic Pigments

1.4 Relationship between Chemical Structure and Pigment Properties

1.5 Physical Characterization of Pigments

1.6 Important Application Properties and Concepts

1.7 Particle Size Distribution and Application Properties of Pigmented Media

1.8 Areas of Application for Organic Pigments

References for Chapter 1

Chapter 2: Hydrazone Pigments (Formerly Called Azo Pigments)

2.1 Starting Materials

2.2 Synthesis of Hydrazone Pigments

2.3 Monohydrazone Yellow and Orange Pigments (Formerly Called Monoazo Yellow and Orange Pigments)

2.4 Dihydrazone Pigments (Formerly Called Disazo Pigments)

2.5 β-Naphthol Pigments

2.6 Naphthol AS Pigments

2.7 Red Hydrazone Pigment Lakes (Formerly Called Red Azo Pigment Lakes)

2.8 Benzimidazolone Pigments

2.9 Dihydrazone Condensation Pigments (Formerly Called Disazo Condensation Pigments)

References for Chapter 2

Chapter 3: Polycyclic Pigments

3.1 Phthalocyanine Pigments

3.2 Quinacridone Pigments

3.3 Vat Dyes Prepared as Pigments

3.4 Perylene and Perinone Pigments

3.5 Diketopyrrolopyrrole (DPP) Pigments

3.6 Indigo, Thioindigo and Thiazine Indigo Pigments

3.7 Various Polycyclic Pigments Derived from Anthraquinone

3.8 Dioxazine Pigments

3.9 Quinophthalone Pigments

3.10 Isoindolinone and Isoindoline Pigments

References for Chapter 3

Chapter 4: Miscellaneous Pigments

4.1 Triarylcarbonium Pigments

4.2 Metal Complex Pigments

4.3 Pigments with Known Chemical Structure Which Cannot be Assigned to Other Chapters

4.4 Pigments with Hitherto Unpublished Chemical Structures

4.5 Organic/Inorganic Hybrid Pigments

References for Chapter 4

Chapter 5: Legislation, Ecology, Toxicology

5.1 Introduction

5.2 Chemicals Legislation

5.3 Ecology

5.4 Toxicology

References for Chapter 5

Reaction Schemes

A1 Starting Materials (Section 2.1)

A2 Synthesis of Hydrazone Pigments (Section 2.2)

A3 Monohydrazone Yellow and Monohydrazone Orange Pigments (Section 2.3)

A4 Dihydrazone Pigments (Section 2.4)

A5 ß-Naphthol Pigments (Section 2.5)

A6 Naphthol AS Pigments (Section 2.6)

A7 Red Hydrazone Pigment Lakes (Section 2.7)

A8 Benzimidazolone Pigments (Section 2.8)

A9 Dihydrazone Condensation Pigments (Section 2.9)

A10 Phthalocyanine Pigments (Section 3.1)

A11 Quinacridone Pigments (Section 3.2)

A12 Perylene and Perinone Pigments (Section 3.4)

A13 Diketopyrrolopyrrole (DPP) Pigments (Section 3.5)

A14 Indigo, Thioindigo and Thiazine Indigo Pigments (Section 3.6)

A15 Various Polycyclic Pigments Derived from Anthraquinone (Section 3.7)

A16 Dioxazine Pigments (Section 3.8)

A17 Quinophthalone Pigments (Section 3.9)

A18 Isoindolinone and Isoindoline Pigments (Section 3.10)

A19 Triarylcarbonium Pigments (Section 4.1)

A20 Metal Complex Pigments (Section 4.2)

List of Commercially Available Pigments

Index

End User License Agreement

List of Tables

Table 1.1

Table 1.2

Table 1.3

Table 1.4

Table 1.5

Table 1.6

Table 1.7

Table 1.8

Table 1.9

Table 1.10

Table 2.1

Table 2.2

Table 2.3

Table 2.4

Table 2.5

Table 2.6

Table 2.7

Table 2.8

Table 2.9

Table 2.10

Table 2.11

Table 2.12

Table 2.13

Table 2.14

Table 2.15

Table 3.1

Table 3.2

Table 3.3

Table 3.4

Table 3.5

Table 3.6

Table 3.7

Table 3.8

Table 3.9

Table 4.1

Table 4.2

Table 4.3

Table 4.4

Table 5.1

Table 5.2

Table 5.3

Table 5.4

Table 5.5

Table 5.6

Table 5.7

Table 5.8

Table 5.9

List of Illustrations

Figure 1.1

Figure 1.2

Figure 1.3

Figure 1.4

Figure 1.5

Figure 1.6

Figure 1.7

Figure 1.8

Figure 1.9

Figure 1.10

Figure 1.11

Figure 1.12

Figure 1.13

Figure 1.14

Figure 1.15

Figure 1.16

Figure 1.17

Figure 1.18

Figure 1.19

Figure 1.20

Figure 1.21

Figure 1.22

Figure 1.23

Figure 1.24

Figure 1.25

Figure 1.26

Figure 1.27

Figure 1.28

Figure 1.29

Figure 1.30

Figure 1.31

Figure 1.32

Figure 1.33

Figure 1.34

Figure 1.35

Figure 1.36

Figure 1.37

Figure 1.38

Figure 1.39

Figure 1.40

Figure 1.41

Figure 1.42

Figure 1.43

Figure 1.44

Figure 1.45

Figure 1.46

Figure 1.47

Figure 1.48

Figure 1.49

Figure 1.50

Figure 1.51

Figure 1.52

Figure 1.53

Figure 1.54

Figure 1.55

Figure 1.56

Figure 1.57

Figure 1.58

Figure 1.59

Figure 1.60

Figure 1.61

Figure 1.62

Figure 1.63

Figure 1.64

Figure 1.65

Figure 1.66

Figure 1.67

Figure 1.68

Figure 1.69

Figure 1.70

Figure 1.71

Figure 1.72

Figure 1.73

Figure 1.74

Figure 1.75

Figure 1.76

Figure 1.77

Figure 1.78

Figure 1.79

Figure 1.80

Figure 1.81

Figure 1.82

Figure 1.83

Figure 1.84

Figure 1.85

Figure 1.86

Figure 1.87

Figure 1.88

Figure 1.89

Figure 1.90

Figure 1.91

Figure 1.92

Figure 2.1

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Figure 2.7

Figure 2.8

Figure 2.9

Figure 2.10

Figure 2.11

Figure 2.12

Figure 2.13

Figure 2.14

Figure 2.15

Figure 2.16

Figure 2.17

Figure 2.18

Figure 2.19

Figure 2.20

Figure 2.21

Scheme 2.1

Scheme 2.2

Scheme 2.3

Figure 2.22

Figure 2.23

Figure 2.24

Figure 2.25

Figure 2.26

Scheme 2.4

Figure 2.27

Figure 2.28

Figure 2.29

Figure 2.30

Scheme 2.5

Figure 2.31

Figure 2.32

Figure 2.33

Figure 2.34

Figure 2.35

Figure 2.36

Scheme 2.6

Figure 2.37

Figure 2.38

Figure 2.39

Figure 2.40

Figure 2.41

Figure 2.42

Figure 2.43

Figure 2.44

Figure 2.45

Scheme 2.7

Figure 2.46

Figure 2.47

Scheme 2.8

Scheme 3.1

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7

Figure 3.8

Figure 3.9

Figure 3.10

Figure 3.11

Figure 3.12

Figure 3.13

Figure 3.14

Figure 3.15

Figure 3.16

Figure 3.17

Figure 3.18

Figure 3.19

Figure 3.20

Figure 3.21

Figure 3.22

Figure 3.23

Figure 3.24

Figure 3.25

Figure 3.26

Figure 3.27

Figure 3.28

Figure 3.29

Figure 3.30

Figure 3.31

Figure 3.32

Figure 3.33

Figure 3.34

Figure 3.35

Figure 3.36

Figure 3.37

Figure 3.38

Figure 3.39

Scheme 3.2

Figure 3.40

Figure 3.41

Figure 3.42

Figure 3.43

Figure 3.44

Scheme 3.3

Scheme 3.4

Figure 3.46

Figure 3.47

Figure 3.48

Figure 3.49

Figure 3.50

Figure 3.51

Figure 3.52

Figure 3.53

Figure 3.54

Figure 3.55

Scheme 3.5

Figure 3.56

Figure 3.57

Figure 3.58

Scheme 3.6

Scheme 3.7

Figure 3.59

Figure 3.60

Scheme 3.8

Scheme 3.9

Scheme 3.10

Scheme 3.11

Scheme 3.12

Scheme 3.13

Scheme 3.14

Scheme 3.15

Scheme 3.16

Scheme 3.17

Scheme 3.18

Scheme 3.19

Figure 3.61

Figure 3.62

Figure 3.63

Scheme 3.20

Scheme 3.21

Figure 3.64

Figure 3.65

Figure 3.66

Scheme 3.22

Scheme 3.23

Scheme 3.24

Figure 3.67

Figure 3.68

Scheme 3.25

Scheme 3.26

Figure 3.69

Figure 3.70

Figure 3.71

Figure 3.72

Figure 3.73

Scheme 3.27

Scheme 3.28

Figure 3.74

Figure 3.75

Scheme 3.29

Scheme 3.30

Figure 3.76

Figure 3.77

Figure 3.78

Scheme 3.31

Scheme 3.32

Figure 3.79

Figure 3.80

Scheme 3.33

Scheme 4.1

Scheme 4.2

Scheme 4.3

Scheme 4.4

Scheme 4.5

Scheme 4.6

Scheme 4.7

Scheme 4.8

Scheme 4.9

Figure 4.1

Figure 4.2

Figure 4.3

Scheme 4.10

Figure 4.4

Figure 4.5

Scheme 4.11

Scheme 4.12

Scheme 4.13

Scheme 4.14

Scheme 4.15

Scheme 4.16

Scheme 4.17

Scheme 4.18

Scheme 4.19

Scheme 4.20

Scheme 4.21

Scheme 4.22

Scheme 4.23

Guide

Cover

Table of Contents

Begin Reading

Chapter 1

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Industrial Organic Pigments

Production, Crystal Structures, Properties, Applications

Fourth, Completely Revised Edition

Klaus Hunger and Martin U. Schmidt

With Contributions byThomas Heber, Friedrich Reisinger, and Stefan Wannemacher

Authors

Dr. Klaus Hunger

Decernis GmbHJohann-Strauß-Str. 3565779 KelkheimGermany

Prof. Dr. Martin U. Schmidt

Johann Wolfgang Goethe-UniversitätInstitut für Anorganische undAnalytische ChemieMax-von-Laue-Straße760438 Frankfurt am MainGermany

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at <http://dnb.d-nb.de>.

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978-3-527-32608-2

ePDF ISBN: 978-3-527-64835-1

ePub ISBN: 978-3-527-64834-4

oBook ISBN: 978-3-527-64832-0

Cover Design Grafik-Design Schulz

The printed edition of this book is printed with P.Y.12, P.R.57:1, P.B.15:3 and P.Bl.7

List of Contributors

Main Authors

Klaus Hunger

DECERNIS GmbH

Johann-Strauß-Str. 35

65779 Kelkheim

Germany

Martin U. Schmidt

Johann Wolfgang Goethe-Universität

Institut für Anorganische und Analytische Chemie

Max-von-Laue-Straße 7

60438 Frankfurt am Main

Germany

With Contributions by

Thomas Heber

Clariant Plastics & Coatings (Deutschland) GmbH

Industriepark Höchst C653

65926 Frankfurt am Main

Germany

Friedrich Reisinger

Clariant Plastics & Coatings (Deutschland) GmbH

Industriepark Höchst C653

65926 Frankfurt am Main

Germany

Stefan Wannemacher

Clariant Plastics & Coatings (Deutschland) GmbH

Industriepark Höchst C653

65926 Frankfurt am Main

Germany

Preface to the Fourth Edition

All chapters in the fourth edition have been thoroughly reviewed, revised, and updated. More than 130 formulae were added or revised. About 170 figures were added. The chapter on legislation, ecology, toxicology was completely rewritten and now represents the latest developments.

Actually “Azo pigments” do not exist. All single-crystal structure analyses as well as spectroscopic investigations reveal that no commercial “Azo pigment” contains an azo group, but they exhibit the hydrazone-tautomeric form instead1). Consequently all commercial “azo pigments” should be called “hydrazone pigments”. This nomenclature has been employed throughout this book. We hope, that the correct denomination “hydrazone pigment” finds its way to all publications on organic pigments as well as to the labelling of products etc.

The properties of organic pigments depend on their crystal structures. Correspondingly all available information on the crystal structures of all industrial organic pigments has now been included and almost every crystal structure is depicted by a figure. The effect of the crystal structure and the polymorphism of a pigment on its colouristic and physical properties is described in detail. The new co-author of this book, Prof. Dr. Martin U. Schmidt, has been researching organic pigments since 1995, with a focus on their polymorphism and their crystal structures.

Several sections have been moved to other chapters in the 4th edition. Most triarylcarbonium pigments and most metal complex pigments are neither hydrazone nor polycyclic pigments, hence their description now appears in chapter 4 (Miscellaneous Pigments). The section on isoindoline and isoindolinone pigments has been moved to chapter 3 (Polycyclic Pigments).

We pay tribute to our deceased colleagues Dr. Willy Herbst, who was the former coauthor of the book, and Prof. Dr. Erich F. Paulus (Goethe University, Frankfurt, formerly at Hoechst AG), who worked on polymorphism and single-crystal structure analyses of organic pigments for 43 years.

The layout process for the fourth edition required considerable effort, both by the authors and the publisher, resulting in more than 10 consecutive proofs within a period of 5 years.

The authors thank Dipl.-Ing. Thomas Heber, Dr. Friedrich Reisinger, and Stefan Wannemacher (all from Clariant) for the review and revision of the sections 1.6 to 1.8 and updates in several other sections. We express our gratitude to numerous present and former colleagues at Clariant for many years of kind and intense cooperation, in particular Dr. Dieter Schnaitmann and Dr. Wolfgang Schwab for information on quinacridones and other polycyclic pigments, Dr. Hans Joachim Metz for information on hydrazone pigments, especially quinazolinediones, and Dr. Hans-Tobias Macholdt for information on non-impact printing. Dipl. Chem. Tanja Trepte (formerly at Goethe University) is kindly acknowledged for drawing the new formulae, and Dr. Stephanie Cronje (Goethe University) for improving the English.

Kelkheim and Frankfurt am Main, 2018

K. Hunger, M.U. Schmidt

Note

1)

The only “real” azo pigments are the naphthalene sulfonic acid pigment lakes P.R.66 and P.R.67, which are unable to form tautomeric hydrazone species because they do not contain a hydroxy group in the ortho-position to the azo group.

Preface to the Third Edition

The second edition of our book has again found a favourable reception worldwide, triggering even a reprint of that edition some time ago. We are therefore pleased to present the third edition, again as a comprehensively reviewed and updated version. Due to the friendly acceptance of the former editions, principle and basic concepts of the book have not been changed.

Although Willy Herbst has resigned from work on this new edition, we were able to win three experts on the applications of organic pigments as new coauthors to help continue maintaining the expected standard of Industrial Organic Pigments.

Together with Heinfred Ohleier, Gerhard Wilker and Rainer Winter of Clariant Deutschland GmbH, we thoroughly reviewed and updated all parts of the book and included many pigments newly launched into the market since the second edition, with all properties and applications which were available to us.

Again, we are grateful for comments, advice and additions from colleagues from chemical companies, especially from Clariant, Ciba Specialty Chemicals and Engelhard USA. Furthermore, we express our gratitude to the publishing team of Wiley-VCH, in particular to Karin Sora, who, as always, accompanied our work with great devotion.

Kelkheim and Frankfurt

January 2004

Preface to the Second Edition

The current trend in the manufacture and use of organic pigments is a steady increase, the present worldwide consumption being estimated as 160 000 tons, with an equivalent value of about 3 billion dollars.

As a result of the favorable reception of the first edition of this book, we decided to maintain its structure and conception to the greatest possible extent in this new edition. Thus, we have tried to include comprehensively all organic pigments available on the market. The book has been thoroughly reviewed and carefully updated with regard to production, properties, test methods, application, chemical formulas, and the list of commercially available organic pigments. We have considered all the information accessible to us about pigments newly launched on the market as well as additional information about pigments described in the previous edition. The list of commercially available pigments was further supplemented by more C.I. Formula numbers and CAS numbers. Section 1.6.1 (Coloristic Properties) has been kindly revised by Dr. Glaser, DPP pigments (3.5) and quinophthalone pigments (3.9) are now included in Chapter 3. The index was completely revised and considerably extended by a great many additional terms.

For several reasons, ranges of pigments have been rationalized in recent years, causing a withdrawal of a considerable number of pigments from the market. The rationale behind the removal of these pigments, when known to us, is given. Since these brands will still be used for some years, for example in automotive repair finishes, we have continued to describe their properties in the new edition.

The introduction of newly developed, especially high-performance pigments, may take a considerable period of time. Owing to the outdoors weathering tests required, the extensive and comprehensive testing procedures of very lightfast and weatherfast pigments for automotive finishes or certain plastics applications may last two years or even longer. Because of the dependence of lightfastness and weatherfastness on the entire application media, correspondingly comprehensive testing procedures have to be performed by the pigment manufacturer, i.e., the paint company or plastics processor. For this reason, high-performance pigments may often take several years to reach the market.

We thank the management and several colleagues of the Division Specialty Chemicals of Hoechst AG for supporting us again by providing relevant information and scientific sources. Furthermore, we express our gratitude to colleagues at Ciba-Geigy AG in Basel for assistance, which greatly helped to improve our knowledge of DPP pigments. We are grateful to several colleagues from other companies for their advice and suggestions.

The cooperation with our publisher, WILEY-VCH, was again a pleasure for us, and we thank Ms. K. Sora and Ms. C. Grossl in particular for their devotion to making this book a successful one.

Hofheim and Kelkheim

April 1997

Preface to the First Edition

Organic pigments - the increasingly most important group of organic colorants worldwide - have never yet been treated comprehensively with respect to their industrial significance and their application properties. In this book we have tried to give an account of the chemistry, the properties, and applications of all commercially produced organic pigments.

This book is intended for all those who are interested in organic pigments, especially chemists, engineers, application technicians, colorists, and laboratory assistants throughout the pigments industry and in universities and technical colleges. We have specifically avoided an in-depth discussion of the underlying scientific and theoretical framework, but there are references to the pertinent literature.

The initial part is devoted to chemical and physical characterization of pigments and discusses important terminology connected with pigment application. This is followed by three chapters describing the chemistry and synthesis, the properties and application of individual pigments. In these chapters pigments are classified according to their chemical structure and listed by their Colour Index Name instead of their trade name. The Colour Index, published by the Society of Dyers and Colourists, lists all those pigments and dyes which have been registered by the pigment and dye manufacturers. The products are listed by their Colour Index (C.I.) Generic Name, followed by a Constitution Number, provided the chemical structure has been published. An example is C.I. Pigment Yellow 1, 11680. The last chapter discusses questions of ecology and toxicology. The literature references listed at the end of each dual-numbered subchapter have been limited to a selection covering the most important topics. The appendix shows general structural equations for the syntheses of individual groups of pigments and lists all pigments mentioned in this book, including the respective CAS (Chemical Abstracts Service) registry numbers.

The technical and fastness properties of different pigments have been assessed by unified, usually standardized test methods. Lightfastness measurements, however, had to be carried out by comparison to the Blue Scale - despite serious objections which are explained in the text. This was the only technique which made it possible to list comparative values for all pigments described in this book.

After careful deliberation we have reluctantly refrained from listing data on pigment economics. Reliable data on organic pigments have only been published in a few countries. Moreover, many of the other data turned out to be either contradictory or so incomplete that it was impossible to elicit reliable information from them.

We are pleased to present here the English version of our book, which is an update of the German edition of 1987, supplemented by all appropriate and newly published data. Also included are those commercial organic pigments which have recently been introduced to the market.

We would like to thank Mrs. Barbara Hoeksema for her work in translating this book.

We would like to express our gratitude to the management of the Fine Chemicals and Colors Division of Hoechst AG for their support and for making the scientific and technical resources available to us. We would also like to thank the numerous colleagues, both at other companies - especially at BASF AG and at Ciba/Geigy AG - and in-house colleagues, who through their stimulation, critique, and suggestions supported us considerably. We would like to express our particular gratitude to Dr. F. Glaser, who wrote Chapter 1.6.1.

Our appreciation is also extended to our families and friends, without whose consideration and patience it would not have been possible to write this book.

It is a pleasure to express our gratitude to the VCH publishing company who helped us greatly through their stimulation and their compliance with many of our wishes.

Frankfurt-Höchst

December 1992

List of Abbreviations

ABS

acrylonitrile-butadiene-styrene

BET

Brunauer, Emmett and Teller

BONA

ß-oxy-naphthoic acid

BP

British patent

CF

copper ferrocyanide

C.I.

Colour Index

CIE

Commission internationale de l'éclairage (International Commission on Illumination)

CIELAB

L*a*b* system of the Commission internationale de l'éclairage

CH

Swiss patent or patent application

(C)PVC

(critical) pigment volume concentration

CuPc

copper phthalocyanine

DE-AS

Deutsche Anmeldungsschrift (German patent application)

DE-OS

Deutsche Offenlegungsschrift (German patent application)

DE-PS

Deutsche Patentschrift (German patent)

DIN

Deutsches Institut für Normung (German Institute of Standardization)

DPP

diketopyrrolopyrrole

DRP

Deutsches Reichs-Patent (German Patent before 1945)

EP

European patent

FATIPEC

Federation of Associations of Technicians for Industry of Paints in European Countries

HALS

Hindered Amine Light Stabilizers

HDPE

high density polyethylene

HOMO

highest occupied molecular orbital

JP

Japanese patent

LDPE

low density polyethylene

LUMO

lowest unoccupied molecular orbital

NAD

nonaqueous dispersion

NC

nitrocellulose

NMP

N-methyl -2-pyrrolidone

O.E.M

original equipment manufacture

PA

polyamide

PBT

persistant, bioaccumulating, toxic

P.B.

Pigment Blue

P.Bl.

Pigment Black

P.Br.

Pigment Brown

P.Gr.

Pigment Green

P.O.

Pigment Orange

P.R.

Pigment Red

P.V.

Pigment Violet

P.Y.

Pigment Yellow

PC

polycarbonate

PCB

polychlorobiphenyl

PCDD

polychlorinated dibenzodioxin

PCDF

polychlorinated dibenzofuran

PDF

pair-distribution function

PE

polyethylene

PET

polyethylene terephthalate

PM

phosphomolybdic acid

PMA

polymethyl acrylate

PMMA

polymethyl methacrylate

PVC

polyvinylchoride

POM

polyoxymethylene

POP

persistent organic pollutant

PP

polypropylene

PS

polystyrene

PT

phosphotungstic acid

PTM

phosphotungstomolybdic acid

PUR

polyurethane

PVC

polyvinyl chloride

QQ

quinolonoquinolone

SAN

styrene-acrylonitrile

SD

Standard Depth of shade

SM

silicomolybdic acid

TEM

transmission electron microscopy

THI

thiazine indigo

US

(In the reference section) US Patent

WO

International patent application

1General

1.1 Definition: Pigments and Dyes

Colourants are classified as either pigments or dyes. Pigments are inorganic or organic, coloured, white or black materials that are practically insoluble in the medium in which they are incorporated. Dyes, unlike pigments, do dissolve during their application and in the process lose their crystal or particulate structure. It is thus by physical characteristics rather than by chemical composition that pigments are differentiated from dyes [1]. In fact, both are frequently similar as far as the basic chemical composition goes, and one structural skeleton may function either as a dye or as a pigment.

In many cases the general chemical structure of dyes and pigments is the same. The necessary insolubility for pigments can be achieved by avoiding solubilizing groups in the molecule or by forming insoluble organic structures. Carboxylic and especially sulfonic acid functional groups lend themselves to the formation of insoluble metal salts (lakes); the formation of metal complex compounds without solubilizing groups and finally suitable substitution may decrease the solubility of the parent structure (e.g. carbonamide groups).

Pigments of many classes may be practically insoluble in one particular medium, yet dissolve to some extent in another. Partial solubility of the pigment is a function of the application medium and processing conditions, especially of the processing temperature. Important application properties of pigments and/or pigmented systems, such as tinctorial strength, migration, recrystallization, heat stability, lightfastness, and weatherability, are often determined by the portion of pigment that dissolves to a minor degree in the vehicle in which it is applied.

Monohydrazone yellow pigments of the Hansa Yellow type (e.g. Pigment Yellow (P.Y.) 1, P.Y.3; Section 2.3.4.2) may serve as an example. Their solubility in air-dried alkyd resin systems is so negligible that they are considered insoluble, which explains their frequent use in such media. Since their solubility increases with increasing temperature, they migrate considerably in vehicles such as various oven-dried varnish systems or in plastics. This results in bleeding or blooming (Section 1.6.3). Strong migratory tendencies preclude their use in such high temperature applications. Even slight temperature changes in the course of pigment incorporation into its application medium may often determine the commercial fate of a pigment. Moreover, the inherent tinctorial properties of a product in a particular vehicle system are sometimes compromised by difficulties such as recrystallization, which arises through a certain solubility of the pigment in its medium.

Under certain circumstances, it may even be advantageous to have a pigment dissolved to some degree in its binder system in order to improve certain application properties such as tinctorial strength and rheological behaviour. Such conditions arise when special amine-treated diarylide yellow pigments are incorporated in toluene-based publication gravure inks (Section 1.8.1.1). In toluene, up to 5% of the amine-treated pigment may be either dissolved or dispersed to a nearly molecular level. This improves the tinctorial strength and decreases the viscosity, which in turn enhances the rheology of the pigmented ink. The performance of a colourant in its role as a commercial pigment is therefore defined by its interaction with the application medium under the conditions that govern its application.

1.1.1 Organic and Inorganic Pigments

In some application areas, inorganic pigments are also used to an appreciable extent, frequently in combination with organic pigments. A comparison of the respective application properties of inorganic versus organic pigments shows some fundamentally important differences between the two families.

Most inorganic pigments are extremely weatherfast (Section 1.6.6) and many exhibit excellent hiding power (Section 1.6.1.6). Their rheology is usually an advantage (Section 1.6.8), being superior to that of most organic pigments under comparable conditions. In white reductions, however, many inorganic pigments have much less strength than organic pigments. With few exceptions such as Bismute Vanadate, Molybdate Red, Chrome Yellow, and cadmium-based pigments, inorganic pigments provide dull shades. Since there are only relatively few inorganic types, the spectral range that is accessible by inorganic pigments alone is very limited. Many hues cannot be produced in this manner.

Inorganic pigments not only exhibit colouristic limitations but also frequently present application problems. Ultramarine Blue, for instance, is not fast to acid, while Prussian Blue must not be exposed to alkalis. Such limitations preclude the application of, especially, Prussian Blue in paints that are to be applied to a basic substrate (e.g. exterior house paints). In the red range of the spectrum, iron oxide red pigments produce weak hues of comparatively little brilliance. Molybdate Reds and Chrome Yellows lend themselves to a host of applications but are nevertheless sensitive to acids and light. There are stabilized versions of such pigments that claim improved lightfastness and acid resistance. These products also claim to be chemically fast to hydrogen sulfide, which affects the brightness of a coating through sulfide formation. However, if the particle surfaces of such types are damaged during the dispersion process, the above-mentioned deficiencies are apparent at the damaged site.

Poor tinctorial strength and lack of brilliance restrict the use of inorganic pigments in printing inks. There are areas of application, however, where it is hardly, if at all, possible to replace the inorganic species by an organic pigment. The ceramics industry, for example, requires extreme heat stability, which precludes the use of organic compounds. Thus, the organic and inorganic classes of pigments are generally considered complementary rather than competitive.

1.2 Historical

The history of pigment application dates back to prehistoric cave paintings, which give evidence of the use of ochre, haematite, brown iron ore, and other mineral-based pigments more than 30 000 years ago. Cinnabar, azurite, malachite, and lapis lazuli have been traced back to the third millenium BC in China and Egypt. With Prussian Blue, in 1704 the first non-natural inorganic pigment was synthesized. It was not until a century later that Thenard produced his Cobalt Blue. Ever increasing expertise and technology led to the production of Chrome Yellow, Cadmium Yellow, several synthetic iron oxides covering parts of the ranges of yellow, red, and black hues, Chrome Oxide Green, and Ultramarine.

Important twentieth-century developments include the addition of Molybdate Red to the series of inorganic synthetic colouring matters in 1936; Titan Yellow followed in 1960.

Later newly developed inorganic pigments have been introduced to the market, such as bismuth–molybdenum–vanadium oxide pigments for lead-free formulation, or cerium sulfide pigments, which can be used as a replacement for cadmium sulfide pigments.

The beginning of organic pigment application dates to antiquity. It is certain that the art of using plant and animal ‘pigments’ to extend the spectral range of available inorganic colourants by a selection of more brillant shades had been practised thousands of years ago. However, for solubility reasons, most of these organic colours would now be classified as dyes rather than pigments. Even in antiquity, they were used not only for dyeing textiles but also, due to their ability to adsorb on mineral-based substrate such as chalk and china clay, for solvent resistant coatings for decorative purposes. These materials later came to be known as lakes or toners. For thousands of years, derivatives of the flavone and anthraquinone series have been the major source of natural colours for such applications.

The beginning of the era of scientific chemistry was marked by the synthesis of large numbers of dyes for textile related purposes. Some of these were also applied to inorganic substrates by adsorption, for use as pigment toners. The commercially available soluble sodium salts of acid dyes were rendered insoluble, an essential property of pigments, by reacting them with the water-soluble salts of calcium, barium, or lead to form lakes. Basic dyes (commercially available as chlorides or as other water-soluble salts), on the other hand, were treated with tannin or antimony potassium tartrate to yield insoluble colourants, that is, pigments. Some of the early commercially important lakes, such as Lake Red C (Pigment Red 53:1) and Lithol Rubine (Pigment Red 57:1), released on to the market in 1902 and 1903, respectively, are still commercially important products (Section 2.7).

Entering the market in the late nineteenth century were the first water insoluble pigments that did not contain acidic or basic groups, namely, the red β-naphthol pigments (Para Red P.R.1, 1885). Falling into the same chemical class are Toluidine Red (P.R.3, 1905) and Dinitroaniline Orange (P.O.5, 1907), two members of this class of pigments that still enjoy commercial importance today. In 1909, Hansa Yellow (P.Y.1) was introduced to the market as the first monohydrazone yellow pigment. The first red Naphthol AS pigments followed in 1912, and the first commercial pioneers of the diarylide yellow pigment range, some of which had been patented as early as 1911 [2], appeared in 1935. Phthalocyanine blue pigments also appeared in 1935, followed by phthalocyanine green pigments a couple of years later [3]. The rapid advances in pigment chemistry led to such important classes of pigments as dihydrazone condensation pigments in 1954, quinacridones in 1955, dihydrazone pigments of the benzimidazolone series in 1960, the isoindolinone pigments in 1964 [4], and the diketopyrrolo-pyrrole pigments in 1986.

1.3 Classification of Organic Pigments

Several classification systems for organic pigments have been proposed over the years. Basically, it seems appropriate to adopt a classification system by grouping pigments either by chemical constitution or by colouristic properties. A strict separation of the two classification systems is not very practical, because the categories tend to overlap; however, for the purposes of this book it is useful to list pigments according to their chemical constitution.

A rough distinction can be made between hydrazone and nonhydrazone pigments. Most nonhydrazone pigments have polycyclic ring systems and are therefore known as polycyclic pigments. The group of hydrazone pigments can be further subdivided according to structural characteristics, such as by the number of hydrazone groups or by the type of diazo or coupling component. Polycyclic pigments, on the other hand, may be identified by the number and the type of rings that constitute the aromatic structure. Furthermore, there is a smaller group of pigments that contains neither a hydrazone moiety nor a polycyclic ring system.

1.3.1 Hydrazone Pigments (Formerly Called Azo Pigments) (Chapter 2)

Hydrazone pigments have the hydrazone group (NHN) in common. Formerly, hydrazone pigments were called ‘azo pigments’, because they were believed to contain the azo group NN. However, all commercial ‘azo’ pigments do not contain an azo group, but a hydrazone group instead (see Chapter 2, Section 2.1 for details). Thus, the correct name is ‘hydrazone pigments’ instead of ‘azo pigments’, and this name is used throughout this book.

The synthesis of hydrazone pigments is economically attractive, because the standard sequence of diazonium salt formation and subsequent reaction with a wide choice of coupling components allows access to a wide range of products. The hydrazone pigments can be subdivided into monohydrazone and dihydrazone pigments.

1.3.1.1 Monohydrazone Yellow and Orange Pigments (Formerly Called Monoazo Yellow and Orange Pigments) (Section 2.3)

Monohydrazone yellow pigments that are obtained by coupling a diazonium salt with acetoacetic arylides as coupling components cover the spectral range between greenish and medium yellow; coupling with 1-arylpyrazolones-5 affords reddish yellow to orange shades.

All members of this pigment family share good lightfastness, combined with poor solvent and migration resistance. These properties define and limit their application. Monohydrazone yellow pigments are used extensively in air-dried alkyd resin and in emulsion paints, and certain inks used in flexo and screen printing. Other applications are in letterpress and offset inks, as well as in office articles.

1.3.1.2 Dihydrazone Pigments (Formerly Called Disazo Pigments) (Section 2.4)

There is a dual classification system based on differences in the starting materials. The first and most important group includes compounds whose synthesis involves the coupling of di- and tetra-substituted diaminodiphenyls as diazonium salts with acetoacetic arylides (diarylide yellows) or pyrazolones (dihydrazone pyrazolones) as coupling components. The second group, bisacetoacetic arylide pigments, are obtained by diazotization of aromatic amines, followed by coupling to bisacetoacetic arylides.

The colour potential of dihydrazone pigments covers the colour range from very greenish yellow to reddish yellow and orange and red. Most show poorer lightfastness and weatherfastness – but better solvent and migration fastness than monohydrazone yellow and orange pigments. Their main applications are in printing inks and plastics, and to a lesser extent in coatings and toners for laser printing.

1.3.1.3 β-Naphthol Pigments (Section 2.5)

β-Naphthol pigments provide colours in the range from orange to medium red. The typical coupling reaction with β-naphthol as a coupling component yields such well-known pigments as Toluidine Red and Dinitroaniline Orange. Their commercial application in paints requires good lightfastness. Solvent resistance, migration fastness and lightfastness are comparable to the monohydrazone yellow pigments.

1.3.1.4 Naphthol AS Pigments (Section 2.6)

These pigments are obtained by coupling substituted aryl diazonium salts with arylides of 2-hydroxy-3-naphthoic acid (2-hydroxy-3-naphthoic acid anilide = Naphthol AS). They provide a broad range of colours from yellowish and medium red to bordeaux, carmine, brown and violet; their solvent fastness and migration resistance are only marginal. Naphthol AS pigments are used mainly in printing inks and paints.

1.3.1.5 Hydrazone Pigment Lakes (Formerly Called Azo Pigment Lakes) (Section 2.7)

In Europe, pigments of this type are known as ‘toners’, but since this term is used differently elsewhere we refer to them as ‘lakes’ throughout this book, although a chemically correct description would be ‘salt type pigments’.

Historically, ‘lakes’ refered to the first type of synthetic organic pigments made from water-soluble dyes by precipitation onto alumina hydrate (aluminium hydroxide).

Laked pigments are formed by precipitating a monhydrazone compound that contains sulfo and/or carboxy groups. The coupling component in the reaction may vary: monohydrazone yellow pigment lakes are based on acetoacetic arylides or 1-arylpyrazolones-5 (Section 2.3.1.2); β-naphthol lakes are derived from 2-naphthol; BONA pigment lakes use 2-hydroxy-3-naphthoic acid (Beta-Oxy-Naphthoic Acid); and Naphthol AS pigment lakes contain anilides of 2-hydroxy-3-naphthoic acid as a coupling component. Lakes may also be prepared from naphthalenesulfonic acids.

Monohydrazone yellow pigment lakes show good migration fastness and heat stability, making them useful products for plastics. Lake Red C is one of the commercially significant β-naphthol lakes. Limited lightfastness, which ranks far behind the non-laked β-naphthol counterparts, along with a tendency to migrate largely restricts their use mainly to the printing inks field.

Most BONA lake pigments provide an extra site for salt formation. Apart from the usual substituents, the diazo components of almost all BONA lake pigments contain a sulfonic acid function. Two acid substituents are thus available to form insoluble salts, which is the form in which these pigments are commercially available. Metal cations such as calcium, strontium, barium, magnesium or manganese combine with the organic anion to produce shades between medium red and bluish red. Their use in printing inks exceeds their increasing use in plastics and paints.

The organic acid group of Naphthol AS pigment lakes is part of the diazo component; a second site for salt formation can be provided by the coupling component. The plastics industry is the main user of such lakes.

Naphthalenesulfonic acid lake pigments are based on naphthalenesulfonic acid as a coupling component; introduction of an additional SO3H function as part of the diazo component is possible.

1.3.1.6 Benzimidazolone Pigments (Section 2.8)

Benzimidazolone pigments feature the benzimidazolone structure, introduced as part of the coupling component. The pigments that are obtained by coupling to 5-acetoacetylaminobenzimidazolone cover the spectrum from greenish yellow to orange; 5-(2-hydroxy-3-naphthoylamino)benzimidazolone as a coupling component affords products that range from medium red to carmine, maroon, bordeaux and brown shades. Pigment performance, including lightfastness and weatherability, is generally excellent. Pigments that satisfy the specifications of the automobile industry are used to an appreciable extent in automotive finishes. Benzimidazolone pigments are also used extensively to colour plastics and high grade printing inks.

1.3.1.7 Dihydrazone Condensation Pigments (Formerly Called Disazo Condensation Pigments) (Section 2.9)

These pigments can formally be viewed as resulting from the condensation of two carboxylic monohydrazone components with one aromatic diamine. The resulting high molecular weight pigments show good solvent and migration resistance and generally provide good heat stability and lightfastness. Their main markets are in the plastics field and in spin dyeing. The spectral range of dihydrazone condensation pigments extends from greenish yellow to orange and bluish red or brown.

1.3.2 Polycyclic Pigments (Chapter 3)

Pigments with condensed aromatic or heterocyclic ring systems are known as polycyclic pigments. The numerous pigment classes that fall into this category do not reflect their actual commercial importance; only a few are produced in large volumes. Their chief characteristics are good light- and weatherfastness and good solvent and migration resistance, but, apart from the phthalocyanine pigments, they are generally also more costly than hydrazone pigments.

1.3.2.1 Phthalocyanine Pigments (Section 3.1)

Phthalocyanine pigments are derived from the phthalocyanine structure, a tetraaza-tetrabenzoporphine. Although this basic molecule can chelate with a large variety of metals under various coordination conditions, today only the copper(II) complexes are of practical importance as pigments. Excellent general chemical and physical properties, combined with good economy, make them the largest fraction of organic pigments in the market today. Copper phthalocyanine blue exists in several crystalline modifications. Commercial varieties include the reddish blue alpha form, as stabilized and nonstabilized pigments, the greenish blue beta modification and, as yet less important, the intense reddish blue epsilon modification. Bluish to yellowish shades of green pigments may be produced by introduction of chlorine or bromine atoms into the phthalocyanine molecule.

1.3.2.2 Quinacridone Pigments (Section 3.2)

The quinacridone structure is a linear system of five anellated rings. These pigments largely have the same performance attributes as phthalocyanine pigments. Outstanding light- and weatherfastness, resistance to solvents and migration resistance justify the somewhat higher market price in applications for high grade industrial coatings, such as automotive finishes, for plastics and special printing inks. Unsubstituted trans-quinacridone pigments are commercially available in a reddish violet beta and a red gamma crystal modification. One of the more important substituted pigments is the 2,9-dimethyl derivative, which affords a clean bluish red shade in combination with excellent fastness properties. Solid solutions of unsubstituted and differently substituted quinacridones and blends with quinacridone quinone resulting in reddish to yellowish orange pigments are commercially available; in contrast, 3,10-dichloroquinacridone as yet enjoys only limited success as a pigment.

1.3.2.3 Perylene and Perinone Pigments (Section 3.4)

Perylene pigments include the dianhydride and diimide of perylene tetracarboxylic acid along with derivatives of the diimide; while perinone pigments are derived from naphthalene tetracarboxylic acid.

Commercially available types provide good to excellent lightfastness and weatherability; some of them, however, darken upon weathering. A number of them have excellent heat stability, which renders them suitable for spin dyeing. They are also used to colour polyolefins that are processed at high temperatures. The list of applications includes high grade industrial coatings, such as automotive finishes, and, to a lesser degree, special printing inks for purposes such as metal decoration and poster printing.

1.3.2.4 Diketopyrrolopyrrole (DPP) Pigments (Section 3.5)

The basic skeleton of this group of pigments consists of two anellated five-membered rings each of which contains a carbonamide moiety in the ring.

This class of pigments presently has some commercially used representatives, one of them with great importance in the market. In full shades and white reductions, the pigments afford shades in the colour range from orange to medium and bluish reds. The pigments are used primarily in high grade industrial coatings, including automotive finishes and in plastics because of their excellent lightfastness and weatherfastness as well as their good heat stability.

1.3.2.5 Thioindigo Pigments (Section 3.6)

4,4′,7,7′-Tetrachlorothioindigo with a reddish violet shade reigns supreme as a pigment amongst the derivatives of this indigo. It can be used for bordeaux shades in automotive refinishes. Thioindigo pigments are generally used in industrial coatings and plastics for their good lightfastness and weatherfastness in deeper shades.

1.3.2.6 Pigments Derived from Anthraquinone (Section 3.7)

Apart from some nonclassified pigments such as Indanthrone Blue (P.Bl.60), the anthraquinone pigments, which are structurally or synthetically derived from the anthraquinone molecule, can be divided into the following four groups of polycyclic pigments.

1.3.2.6.1 Anthrapyrimidine Pigments

The commercially leading member of this class is Anthrapyrimidine Yellow, which in very light white reductions affords a greenish to medium yellow with excellent weatherfastness. It lends itself primarily to application in industrial coatings such as automotive metallic finishes or to modification of the shades of automotive finishes.

1.3.2.6.2 Flavanthrone Pigments

Flavanthrone Yellow, the only commercially used flavanthrone, is a moderately brilliant reddish yellow. Excellent lightfastness and weatherfastness, combined with good solvent and migration resistance, make this pigment an attractive supplement to Anthrapyrimidine Yellow, mainly in the automotive finish industry.

1.3.2.6.3 Pyranthrone Pigments

Commercial attention focuses on the derivatives of the pyranthrone molecule at a varying level of halogenation. Most are orange, but others exhibit a dull medium to bluish red shade. Owing to their good weatherfastness pyranthrone pigments are used for high grade industrial finishes.

1.3.2.6.4 Anthanthrone Pigments

Dibromoanthanthrone is the only commercial pigment within this group. Qualities such as outstanding light- and weatherfastness justify the relatively high cost for application in high grade industrial coatings such as automotive finishes. The transparent pigment provides shades of scarlet for metallic finishes.

1.3.2.7 Dioxazine Pigments (Section 3.8)

Dioxazine pigments are based on triphenodioxazine, a linear system of five anellated rings. Apart from Pigment Violet 37, the commercially most representative one is Pigment Violet 23, an extremely lightfast and weatherfast compound with good to excellent solvent and migration resistance. Applications include the pigmentation of coatings, plastics, printing inks, as well as spin dyeing. Apart from producing violet shades, the pigment also lends itself to the shading of phthalocyanine blue pigments in colourations, particularly in coatings. It is also used to tone the light yellowish shade of titanium dioxide in whites and in shading carbon blacks that have a brownish cast.

1.3.2.8 Quinophthalone Pigments (Section 3.9)

Quinophthalone pigments have a polycyclic structure derived from quinaldine and phthalic anhydride. A few members of this class have gained commercial recognition for their very good temperature resistance. The main markets for their mostly greenish yellow shades are in the plastics and coatings industries.

1.3.2.9 Isoindolinone and Isoindoline Pigments

Although of comparatively good light- and weatherfastness and solvent and migration resistance, only a few members of the isoindolinone and isoindoline families are commercially available as pigments. Chemically classified as heterocyclic azomethines, these pigments produce greenish to reddish yellow hues. Isoindolinone pigments are preferably supplied for the pigmentation of plastics and high grade coatings.

1.3.3 Miscellaneous Pigments (Chapter 4)

There are a few pigment classes that can neither be sorted under hydrazone nor under polycyclic pigments. This group includes triarylcarbonium pigments and metal complex pigments as well as a number of individual pigments not belonging to a larger class of commercial pigments.

1.3.3.1 Triarylcarbonium Pigments (Section 4.1)

There are two groups of triarylcarbonium pigments: (i) inner salts of triphenylmethane sulfonic acids and (ii) complex salts with heteropolyacids containing phosphorus, tungsten, molybdenum, silicon or iron.

The first group is characterized by poor lightfastness and limited solvent resistance. Alkali Blue is the only member of this group with considerable commercial value. To tone black printing inks, Alkali Blue is used in combination with the very high-absorbing carbon black pigment, which increases its lightfastness considerably.

The second group includes the complex salts of basic pigments that are common in the dyes industry, such as Malachite Green, Methylene Violet, Crystal Violet or Victoria Blue with certain heteropolyacids. Despite the disadvantages of comparatively poor solvent resistance and limited lightfastness, these pigments are used for their excellent colour brilliance and clarity of hue – properties that exceed those of any of the other known organic or inorganic pigments. Such features make these types, whose lightfastness satisfies commercial requirements, suitable candidates for the printing inks industry and especially for packaging inks.

1.3.3.2 Metal Complex Pigments (Section 4.2)

Most metal complex pigments contain either an azo group (NN) or an azomethine (CHN) moiety. The metal is usually nickel or copper, and less commonly cobalt or iron(II).

Only a few azo metal complexes are available as pigments. They exhibit green or greenish yellow shades. Most of these are very lightfast and weatherfast.

Commercial azomethine complex pigments afford yellow, orange or red shades. Those species that provide the required lightfastness and weather resistance are used in automotive finishes and other industrial coatings.

1.4 Relationship between Chemical Structure and Pigment Properties

In this chapter, the correlation between chemical constitution and pigment performance is outlined in terms of empirical rules. These correlations are essentially applicable, independently of the application medium, to all industrial uses of pigments.

While the properties of (soluble) dyes are determined almost exclusively by their chemical constitution, application characteristics of pigments – which are by definition insoluble in the medium in which they are applied (Section 1.1) – are largely controlled by their crystalline constitution, that is, by their physical characteristics. This is discussed in the next chapter.

The application properties of a pigment are basically governed by its chemical constitution, which in turn has a bearing on the crystal structure, thus determining the physical parameters. This seemingly straightforward correlation is complicated by the fact that various crystal structures (modifications, see Section 1.5.3) may evolve from one and the same chemical constitution. Apart from knowledge about the chemical constitution of a compound, only extensive insight into the crystal structures and their solid-state physics thus allows certain predictions as to the application properties of the pigment.

This chapter discusses the influence of the chemical constitution on the hue, tinctorial strength, lightfastness, weatherfastness, solvent resistance, and migration resistance of a pigment. The systematic synthesis of a pigment with certain defined target properties is only possible to a very limited extent. Only with a reliable crystal-structure prediction can a prediction of the pigment's properties be made.

1.4.1 Hue

The appearance of colour in a molecule is associated with electronic excitation [5–9] caused by absorption of incident electromagnetic radiation in the ultraviolet and visible regions of the spectrum. Electrons are elevated from the ground state energy level to an excited state by absorbing selected frequencies of incident visible light, thereby giving the molecule the shade of the resulting complementary colour. The fact that each electronic excitation is accompanied by a battery of rotational and vibrational transitions is responsible for the appearance of more or less broad absorption bands. An absorption band is said to undergo a bathochromic shift if a comparison of spectra shows that it has moved to longer wavelengths; a hypsochromic shift involves movement to shorter wavelengths.

The hue is primarily defined by the pattern of chromophores, a conjugated π-system, which is responsible for the absorption of visible light. For transition-metal containing compounds, for example copper phthalocyanine, the electrons of the metal play a role, too.

Substituents with lone electron pairs, such as alkoxy, hydroxy, alkylamino and arylamino groups, are known as electron donors. Alkyl groups, despite the absence of such free electron pairs, are also considered to be electron donors. Functional groups with conjugated π-electron systems, such as NO2, COOH, COOR, SO2NH2 or SO2Ar, act as electron acceptors.

In discussing substituents of hydrazone pigments, both electron donors and electron acceptors are effective particularly as parts of the diazo component; that is, they are located in the conjugated part of the system. In these positions they usually cause a bathochromic shift of the absorption band with the longest