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Basics of Coating Technology

Prof Dr Artur Goldschmidt and Dr Hans-Joachim Streitberger

BASF Handbook

Basics of Coating Technology

3rd Revised Edition

Prof Dr Artur Goldschmidt and Dr Hans-Joachim Streitberger

BASF Handbook

Basics of

Coating Technology

3rd Revised Edition

Foreword to the 3rd
Revised Edition

Glasurit’s “Paints and Coatings” handbook has been a standard work in the field of coating materials since it was first published in 1934. The latest German edition appeared in 2014 and serves as the basis for this third English edition, which is sponsored by BASF Coatings. Compared with its 2007 predecessor, this third edition contains more up-to-date market data and incorporates new raw materials, new application technologies, new legislative developments, mainly in Europe, as well as modern coating processes.

The main new developments covered in the raw materials and coatings sector are nanotechnology, polyurethane dispersions for water-borne coatings and smart coatings. As for pretreatment processes, application methods and recovery techniques, the latest advances here include workpiece rotation during electrocoating, the integrated paint process and new methods for handling overspray in the automotive industry. More than 200 new references have been added and some 500 others updated.

The proven arrangement of chapters has been left unchanged.

The handbook starts logically with a brief historical summary of painting, its economic and technical significance and the social framework underpinning the industry. Next comes a chapter on raw materials, product composition, the various production processes and the principles behind product formulation. Descriptions are then given of the properties of the liquid and solid coating materials employed in the various applications. This is followed by a chapter dealing with the theoretical aspects of coating compositions. Applications are then explained for the reader against the background of the current major industrial coating processes. This chapter clearly shows just how important the substrate is because of the impact it has on the coating outcome. A chapter follows dealing with the demands on environmental compliance, health, safety and quality as specified in current legislation, mainly in Europe and Germany. After that, the reader is taken on a journey through various sectors of the paint and coatings industry, accompanied by numerous examples and illustrations. This chapter will be of particular interest for newcomers to the industry and practically-minded readers alike. The book concludes with tables of selected standards, explanations of physical symbols, useful websites, definitions of terms and a comprehensive index round.

Literature references are provided for readers seeking more in-depth information. These are to be found at the end of each chapter and are repeated on occasion. Many of the comments and scenarios are based on experience gained by BASF Coatings and are not directly attributable.

We would like to thank BASF Coatings for making this edition possible, along with countless persons for their support and invaluable tips. Special thanks are due to Dr Walter Jouck, Dr Peter Betz, Sabine Rüttgers, Rolf Döring, Jürgen Book, Heike Thöne and Dr Peter Bachhausen from BASF Coatings. We are indebted to Bernd Reinmüller,

Director at the German DIN Institute for the trouble he took to ensure that the standards listed are up to date.

Finally, we would like to express our gratitude to the many companies which kindly provided us with pictures and charts for publication.

Prof Dr Artur Goldschmidt and Dr Achim Streitberger

Paderborn and Münster, November 2017

Contents

Introduction

Coating Materials

Coatings

Coating Technology

Safety, Environmental Protection and Health

Principles of Quality Management

Coating Industries

Industrial Standards

Appendix

10 Index

Contents

Introduction

1.1 Definition, Tasks and Economic Importance

1.2 Retrospective

1.3 References

Coating Materials

2.1 Raw Materials

2.1.1 Film Forming Agents

2.1.1.1 Natural Materials

2.1.1.2 Synthetic Resins

2.1.2 Solvents

2.1.2.1 Theory of Solubility

2.1.2.2 Physical Properties

2.1.2.3 Chemical and Physiological Properties

2.1.2.4 Important Solvents for Paints

2.1.3 Pigments and Extenders

2.1.3.1 Physical Principles behind Chroma and Hiding Power

2.1.3.2 The most Important Pigments for Coating Materials

2.1.3.3 Extenders

2.1.4 Plasticisers and Additives

2.1.4.1 Plasticisers

2.1.4.2 Additives

2.1.5 Nanoproducts

2.1.5.1 Description and Definition

2.1.5.2 Synthesis of Nanoproducts

2.1.5.3 Sample Applications

2.1.5.4 Outlook

2.1.6 Summary

2.2 From Raw Material to Coating Material

2.2.1 General Rules on Drawing up Formulations

2.2.1.1 Purpose and Quality

2.2.1.2 Production Resources, Application Systems and Object to be Painted

2.2.1.3 Function in the Paint System

2.2.1.4 Cost Effectiveness and Availability

2.2.1.5 Occupational Health, Safety and Environmental Protection Regulations

2.2.2 Material Flow in a Paint Factory

2.2.3 Theory of Dispersion

2.2.3.1 Pigment-Specific Properties for Dispersion Processes

2.2.3.2 Wetting and Separation of Agglomerates

2.2.3.3 Stabilisation of Pigment Dispersions

2.2.3.4 Optimum Mill Base Formulation

2.2.4 Production of Coating Materials

2.2.4.1 Processing Sequences in a Paint Plant

2.2.4.2 Agitation and Agitators

2.2.4.3 Dispersing and Dispersers

2.2.4.4 Separation Processes in the Manufacture of Paint

2.2.5 Summary

2.3 Characterisation of Coating Materials

2.3.1 Measurement Accuracy

2.3.2 Testing Raw Materials and Coating Materials

2.3.2.1 Safety and Environment-Related Performance Indicators

2.3.2.2 Chemical Characterisation

2.3.2.3 Physical Indicators

2.3.3 Pigment-Specific Tests

2.3.3.1 Indicators of the Pigment as a Raw Material

2.3.3.2 Tests with the Pigmented Coating Material

2.3.4 Processability of Coating Materials

2.3.5 Summary

2.4 Literature

Coatings

3.1 From Coating Material to Coating: Film Formation

3.1.1 Wetting and Levelling

3.1.2 Solidification of the Film

3.1.2.1 Physical Drying

3.1.2.2 Chemical Curing

3.1.2.3 Flow Patterns in the Solidifying Film

3.1.3 Film Shrinkage

3.1.4 Special Features of High Solids Paints and Water-Borne Paints

3.1.5 Monitoring the Film Forming Process with Measuring Instruments …

3.1.5.1 Levelling and Sagging

3.1.5.2 Film Formation by Air Drying Paints

3.1.5.3 Indirect Methods

3.1.6 Summary

3.2 Properties and Testing of Coatings

3.2.1 Film Thickness

3.2.1.1 Wet Films

3.2.1.2 Dry Films

3.2.2 Dry Film Density

3.2.3 Measurement of Voids in Coating Films

3.2.4 Visual Properties

3.2.4.1 Gloss

3.2.4.2 Colour and Colourimetry

3.2.5 Mechanical Properties

3.2.5.1 Adhesion

3.2.5.2 Elasticity

3.2.5.3 Hardness

3.2.5.4 Abrasion Resistance and Mar Resistance

3.2.5.5 Other Tests

3.2.6 Summary

3.3 Durability of Coatings

3.3.1 Fundamental Features of Ageing

3.3.2 Ageing Tests

3.3.2.1 Methods for Testing Surface Durability

3.3.2.2 Corrosion Protection Tests

3.3.2.3 Chemical Resistance

3.3.3 Summary

3.4 Literature

Coating Technology

4.1 Influence of the Substrate

4.1.1 Wood and Wood Materials

4.1.1.1 Wood as a Material

4.1.1.2 Wood as a Workpiece

4.1.1.3 Pretreatment of Wood

4.1.1.4 Surface Finishing of Wood Panels

4.1.2 Metallic Materials

4.1.2.1 Properties of Metals

4.1.2.2 From the Material to the Workpiece

4.1.2.3 Pretreatments

4.1.3 Plastics

4.1.3.1 Types of Plastics and their Properties

4.1.3.2 Pretreatments

4.1.4 Mineral Substrates

4.1.4.1 Concrete, Mortar, Plaster

4.1.4.2 Glass

4.1.5 Other Substrates

4.1.5.1 Rubber

4.1.5.2 Leather

4.1.6 Workpiece Design and Coatability

4.1.7 Summary

4.2 Paint Processing

4.2.1 Processing of Wet Paints

4.2.1.1 Dip Coating (Object Taken to Paint)

4.2.1.2 Brushing, Manual and Mechanical Roller, Flow and Curtain Coating Methods (Paint Applied Directly to the Object)

4.2.1.3 Spray Process: Paint Applied Indirectly to the Object

4.2.1.4 Paint Supply Systems

4.2.1.5 Booth Conditioning and Overspray Elimination

4.2.1.6 Automated Systems and Robots for Paint Processing

4.2.1.7 Conveyors

4.2.1.8 Paint Removal

4.2.2 Processing of Powder Coatings

4.2.2.1 Retrospective

4.2.2.2 Plant and Equipment Details

4.2.2.3 Powder Coating Materials

4.2.2.4 Powder-Specific Test Methods

4.2.3 Summary

4.3 Drying and Curing

4.3.1 Film Formation by Heat Transfer

4.3.1.1 Theory

4.3.1.2 Oven Design

4.3.2 Curing by UV and Electron-Beam Radiation

4.3.3 Summary

4.4 Literature

Safety, Environmental Protection and Health

5.1 Legislative Framework

5.2 Safety

5.2.1 Manufacturing

5.2.2 Storage

5.2.3 Transportation

5.2.4 Application

5.3 Environmental Protection

5.3.1 Exhaust Air

5.3.2 Wastewater

5.3.3 Recycling and Disposal

5.4 Health

5.5 Ecobalances

5.6 Environment-Compatible Paints and Coatings

5.6.1 Low-Emissions Coatings

5.6.1.1 High Solids

5.6.1.2 Water-Borne Paints

5.6.1.3 Powder Coatings

5.6.1.4 Radiation Curable Paints and Coatings

5.6.1.5 Other Coating Systems

5.6.2 Biobased Coating Systems

5.6.3 Foil Coating

5.7 Economics of Coating Processes

5.8 Literature

Principles of Quality Management

6.1 Evolution of Quality Concepts over Time

6.2 Defects in Coating Processes and Applied Coatings

6.2.1 Identifying Defects and their Causes

6.2.2 The Most Frequent Causes of Surface Defects

6.2.3 Summary

6.3 Material Control

6.4 Defect Prevention by Process Control and Control Loops

6.5 Quality Management

6.6 Literature

Coating Industries

7.1 Automotive OEM Coating

7.1.1 Pretreatment

7.1.2 Electrocoating

7.1.3 Seam Sealant and Underbody Protection

7.1.4 Primer Surfacer

7.1.5 Topcoat Application

7.1.6 Repair in Automotive OEM Lines

7.1.7 Outlook

7.2 Automotive Refinishing

7.3 Automotive Supply Industry

7.4 Coil Coating

7.5 Commercial Vehicles

7.6 Mechanical Engineering

7.7 White Goods

7.8 Building Supplies

7.9 Rail Vehicles

7.10 Wood Coating

7.11 Other Fields of Application

7.11.1 Protection of Structures

7.11.2 Steel Furniture

7.11.3 Aviation Industry

7.11.4 Electrically Insulating Coatings

7.11.5 Communications Equipment

7.11.6 Road Marking paints

7.11.7 Shipbuilding

7.11.8 Wind Energy

7.11.9 Smart Coatings

7.11.10 Miscellaneous Coating Applications

7.12 Literature

Standards

8.1 General Information on Standardisation Work

8.2 Selection of DIN Standards for the Paints and Coatings Industry and their Circle of Users

8.2.1 Standards by Numerical Order

8.2.1.1 Standards on Terminology

8.2.1.2 Standards on Coating Materials

8.2.1.3 Standards on Coatings

8.2.1.4 Standards on Aluminium

8.2.1.5 Standards on Coil Coatings

8.2.1.6 Standards on Galvanised Steel

8.2.1.7 Standards on Wood Outdoors

8.2.1.8 Standards on Anticorrosion Protection of Steel Structures

8.2.1.9 Standards on Nuclear Facilities

8.2.1.10 Standards on Aerospace

8.2.1.11 Standards on Exterior Masonry and Concrete

8.2.1.12 Standards on Shipbuilding

8.2.1.13 Dispersion Coatings for Indoors

8.2.1.14 Synthetic Resin Plasters

8.2.1.15 Powder Coatings

8.2.1.16 Road Marking Paints

8.2.1.17 Radiator Coatings

8.2.1.18 Surface Preparation

8.2.1.19 External Thermal Insulation Composite Systems (ETICS)

8.2.1.20 Colourimetry

8.2.1.21 DIN Reports

8.2.2 Standards by Keyword

8.3 Literature

Appendix

9.1 List of Physical Constants

9.1.1 Latin Symbols

9.1.2 Greek Symbols

9.2 Internet Addresses of Interest to the Coatings World

9.2.1 Organisations/Associations/Authorities

9.2.2 Publications/Information

9.2.3 Institutes/Universities

9.2.4 Miscellaneous

9.3 Acronyms/Abbreviations

Authors

Index

1 Introduction

1.1 Definition, Tasks and Economic Importance

The task of coating technology is to provide surface protection, decorative finishes and numerous special functions for commodities and merchandise by means of organic coatings. Many everyday products are only made usable and thus saleable because of their surface treatment. For this, the right coating formulations, production plant, coating material and suitable coating processes for the product must be available. However, the level of quality attainable via the coating process is not solely a function of the coating material. The object to be coated, along with its design, specific material treatment and an appropriate application method, are further variables which play a significant role. In addressing the ongoing tasks of quality optimisation and rationalisation while minimising the impact on humans and the environment, it is vital that the dependencies mentioned above be not only recognized but also taken into account as the framework shaping the conditions in which work advances from development through to application. Coating technology, therefore, is an interdisciplinary subject.

Figure 1.1.1: Coated everyday objects

Source: VdL

Paints and coating materials are not end products, but merely starter or intermediate products which, for the above-mentioned reasons, require a skilled and conscientious user if they are to be converted into the actual end product, namely the coating itself. Only the cured coating, which in many cases is a system of several individual coats, can meet the wishes invested in and the requirements demanded of the coated products.

Figure 1.1.2: Factors determining the quality of coatings

Two of the most important of the many functions which coatings have to meet are protection and decoration. Others worth noting are the informative tasks and the achievement of special physical effects. The conspicuousness of emergency service vehicles, the camouflaging of military equipment, and road or airport markings are just some of the informative tasks required of coatings. Colour markings enable areas or spaces to be clearly signed or divided. Colour coding helps to indicate the contents of containers and the materials being conveyed in pipes. Optical effects induced by coloured or metallic pigments lend a coating a particular optical attraction. Deliberately generated surface textures such as scars or wrinkles expand the range of effects which can be achieved. The use of colour schemes based on the known physiological and psychological effects of colours also contributes in various ways to improved working conditions and enhanced safety wherever work is done in rooms and on machines. Functional pigments produce colours that vary with temperature, for example as a result of their thermochromic properties, and therefore afford an indirect way of measuring the temperatures of objects.

The most important task of coatings, in economic terms, is surface protection. Thus, coatings help to retain value and improve the usability properties of almost all products and so are of huge economic significance. Particular mention should be made of the protection of metal goods that acquire lasting anticorrosive protection only when they have been painted.

It is vital in this regard, e.g. in the automotive sector, for the resistance of the coating system to external, sometimes aggressive natural and anthropogenic atmospheric influences such as tree resins, bird droppings, acids, alkalis, salts and organic solvents, to be guaranteed.

The protective function of paint on cars must not be impaired even under extreme mechanical impact, such as stone chippings thrown up from the road by traffic or by brush action in carwashes.

Furthermore, coatings must withstand combined, i.e. physical and chemical, effects to which objects are subjected, for example, in different weather conditions. The interaction of sunshine, rain, heat and frost, combined with emissions from heating systems and internal combustion engines, ozone and salt fog makes great demands on a coating’s resistance and protective properties.

However, a surface protection coating can also be applied in order to meet quite different requirements. Floors and steps can be made non-slip, and their utility value enhanced, by means of rough or high-grip coatings. By contrast, surface friction can be reduced by using smooth coatings to produce a high degree of slip. Flammable materials can be rendered safe by means of flame retardant coatings. Antibacterial coatings help keep surfaces sterile in production and storage facilities in dairies and breweries and prevent the growth of barnacles and algae on ships’ hulls. In the electrical engineering sector, insulating coatings provide effective and lasting insulation for wire, windings and condenser materials. On the other hand, conductive coatings can be used to make insulating substrates electrically conductive or even to print electrical circuits. Furthermore, organic coatings can help to reduce noise pollution. Acoustic insulation coatings for machines and underbody protection coatings for passenger cars are examples of this.

This broad spectrum of requirements explains why no single coating material can satisfy every wish simultaneously and in the same way. The goal of providing coating materials for the lasting protection, decoration and improvement of objects made of wood, metal, plastic or mineral materials at reasonable prices can be met only by adopting different formulations based on a range of materials and material combinations. Each of these combinations targets a limited field of substrates, a selected application method and a specific profile of film properties.

Figure 1.1.3: Regional division of the market for paint and coatings in 2010

Coating technology is used in metal processing, in the manufacture of plant and machinery and in the electrical engineering industry. All kinds of road and rail vehicles, ships and aircraft are important objects which require painting or coating. Effective surface protection by means of paints and coatings is also indispensable in the civil engineering sector, for steel and concrete structures and in wood processing. Even plastics and leather require coating in many cases. Modern paper, plastic and sheet-metal packaging materials would be inconceivable without the protection and decoration afforded by coatings.

The global paint and coatings market reflects economic developments in the regions. It is most highly developed, for example, in the triad of North America, Europe, and South East Asia. Per capita consumption of paints and coatings in these regions is approx. 4.5 kg. Growth in coatings consumption is determined by economic development in the various regions and countries [1.3.1].

The broad field of applications for coatings and their widespread use are explained by the high value and great benefits which they offer. The fact that there are few objects which do not require coating is an indication of the enormous importance of coating technology. It would present an incomplete picture to evaluate this importance merely in terms of the 30.5 million tonnes of coating materials manufactured worldwide in 2010 with a value of some 80 billion euros (Figure 1.1.3).

Although quoting the quantities of coating materials is not a direct indication of the added value of industrial commodities, it does permit that area to be calculated which can be protected or decorated by means of coating materials, with due allowance for the film thickness to be applied. An annual production quantity of 30.5 million tonnes (see above) is enough to coat a surface area of some 340,000 km2 in a wet film 100 μm (0.1 mm) thick. That is equivalent to about 3/4 of the surface area of Germany. The same quantity of paint applied to a 10 m wide strip in a film thickness of 100 μm, on the other hand, would stretch from the earth to the moon about 100 times or go around the world 650 times.

A more meaningful evaluation would consider the value of the effectively protected and improved products. On the assumption that painting or coating the goods produced generates an added value of 20 % in the form of extended service life and increased attractiveness, this translates to 140 billion euros for the German market in 2012, or 70 times the value of the paints and coatings sold.

The division of the market into branches and segments is not uniform around the world. A number of such divisions, however, seem to agree on certain segments, such as decorative paints, general industrial paints, automotive paints, and printing inks.

Figure 1.1.4: Worldwide coatings market in 2010 by segments

The largest market for paints and coatings, at 54 %, is that of decorative paints. This is followed, at 38 %, by the market for the industrial coating of a huge range of objects, from compact discs via plastic bumpers for cars to rail vehicles. Automotive coating lines and refinishing body shops are each clearly defined segments with a high technological value, though of less significance in terms of volume sales. Although not shown in Figure 1.1.4, printing inks represent approx. 4 % of global demand for coating materials and are a separate segment in technological and marketing terms, though not from the point of view of their composition.

Figure 1.1.5: Production of coatings in Germany from 2006 to 2010

The size of the European market in 2011 was 9.4 million tonnes. It has undergone a slight shift towards industrial coatings and printing inks compared with the sectoral division in the rest of the world. Germany leads with a consumption of approx. 1.5 million tonnes, ahead of Italy, France, the UK and Spain, which are all in the range between 0.8 and 1.0 million tonnes. The North American market (NAFTA) had a volume of 6.6 million tonnes in 2010 and is served by about 800 companies.

Figure 1.1.6: German coatings market in 2010 by product classes

Source VdL

Figure 1.1.5 gives an overview of the economic development of the paint and coatings industry in Germany since 2006 which is closely linked to the country’s overall economic development.

One of the characteristic features of coatings technology in addition to coatings consumption is the ongoing high energy consumption for processing coatings which is estimated at approx. 200 billion kWh annually worldwide. This figure is the equivalent of the energy content of approx. 30 million tonnes of crude oil. If the raw materials required for paint production are also added to this figure in the form of crude oil equivalents, the result is a total crude oil requirement of approx. 120 million tonnes for the global manufacture and processing of coating materials, or some 3 % of global annual crude oil extraction of approx. 4 billion tonnes in 2012.

The legal requirements imposed on environmentally compatible coating processes have led to the greater use of appropriate coating materials over the last 20 years. These include, in particular, solvent-free powder coatings, water-borne paints, in which organic solvents are replaced in whole or in part by water, high solid paints and radiation-curable paints, which are processed either in aqueous solution or completely without conventional solvents but with the aid of low-molecular reactive thinners. Statistics from the Association of the German Paint Industry (VdL) show that these coatings have achieved the greatest growth over the last 10 years.

As a result of stricter legislation and ongoing improvements in our knowledge of their toxicology, the raw materials are having to be replaced regularly, with all the attendant development costs, if the quality standard achieved is to be maintained.

As far as energy consumption is concerned, there is still a need to be more economical in the use of raw materials and energy. A proportion of the material is lost en route to the finished coating. Spray application, which is specified for many objects to be painted because of its optical attractiveness and range of colours, is prominent in this regard. As far as coating of wood and plastics is concerned, the more effective electrostatic spray methods have not yet found universal acceptance. In addition, paint lines lose substantial quantities of heat energy. In recent years a number of developments have increased the efficiency of coating processes to such an extent that growth in the paint and coatings market in the industrialized countries has only just been below the growth level of the gross domestic product (GDP).

As a result of the use of solvents as an application aid for coatings with an average organic solvent content of 50 %, it has been estimated that additional hydrocarbon emissions of approx. 200,000 tonnes occurred in Germany alone in 2007 [1.3.2].

Whereas organic emissions from motor vehicles have been successfully reduced to less than 1/3 of their previous level in the last 30 years by the introduction of the catalytic converter, successes in coating technology have been much more modest so far by comparison. Despite the use of water-borne paints and powder coatings, including by small and medium-sized enterprises after the enactment of the EU VOC (volatile organic compounds) directive of 1999 and its implementation in Germany under 31 BImSchG (BundesImmissionsSchutzGesetz = Federal Immission Control Act), the German Ministry of the Environment estimates that 30 % of all solvent emissions in 2020 will stem from the paints and coatings industry [1.3.3].

Manufacturers and processors of paints and coatings have substantial gains in terms of occupational health and safety. For some time, the chemical industry, for example, has led the accident statistics in Germany for the industry in having the least number of incidents. Health risks posed by paints and coatings are being kept as low as possible through REACH [1.3.4] and the Biocides Ordinance [1.3.5] in Europe and through the Clean Air Act (CAA) and the Toxic Substances Control Act (TSCA), legislation and civic engagement in North America, and these have brought about substantial changes in coatings technologies and formulations.

Figure 1.1.7: Various factors determining the final coating result of the spray application process

An analysis of this situation reveals that manufacturers and consumers of paints and coatings, though occupying different value added stages, are highly interconnected. Manufacturers develop and supply coatings materials to the consumers who, by applying the products, induce physical, physico-chemical and chemical processes that convert them into an adhering, mechanically solid and, at the same time, flexible coating.

The chemical path by means of which the raw material becomes a finished coating starts at the raw materials or paint manufacturer and is then deliberately interrupted before being taken up again during application by the paint consumer. Although the performance profile of a coating is initially shaped by the paint and thus by the paint manufacturer, it is the processor who actually generates the finished properties. The industrial scale coating of consumer goods is therefore a joint effort between paint and coatings manufacturers and processors.

Paint manufacturers who really know their job not only are responsible nowadays for developing, manufacturing and selling paint. Their task also includes creating the conditions for successful painting through the provision of a permanent technical presence and support. This relates primarily to materials and processes, but also extends to detailed environmental protection and occupational safety issues. Paint manufacturers offer a package, as it were, in which the material is just one component among many (see Figure 1.1.7). A consequence of this in past years has been that the responsibility for producing a coating outcome in the required quality has increasingly been transferred into the hands of the paint supplier (see Chapter 7.1.7).

Apart from the technical tasks of manufacturing and processing coating materials, particular attention needs to be paid to quality assurance methods. Quality assurance provides the link between production and R&D and sales within a company. Production must be capable of reproducibly providing the quality demanded by the customer, while sales must identify the total costs in order that appropriate prices may be obtained.

However, paint manufacturers face specific problems because they are expected to produce material of constant quality and, at the same time, paints of constant processability. This is the only way to create the best conditions for achieving a uniform result in the painted article. This means that there is more to the production of paint and coatings than merely manufacturing a product whose composition is identical with a defined standard. Rather, since physical variables can only rarely serve as criteria for the practical properties of coatings, paint testing of necessity must include simulating the application method used by the processor of these materials. This gives rise to a large number of different test methods because of the very wide range of specification conditions and the different requirements on the coating process resulting from them. Standardising these tests and reducing their overall number are also a priority task for all concerned.

Quality and costs of a coating are defined, as mentioned earlier, not only by the paint material and an appropriate application method but also and significantly by the substrate, i.e. by the material and the design of the object to be painted. It is therefore clear that it is extremely important to address surface treatment and the selection and design properties of the material during the product design stage and to incorporate these features into the overall planning.

Coating technology is therefore a complex marriage of chemical, physical, process-engineering, environmental, toxic and economic variables. This discipline is in a constant state of change as a result of technical progress and is further accelerated by legislative requirements. It is therefore incumbent on companies to link well known features with new knowledge. Industrial coating technology can only be fully understood if, in addition to detailed knowledge of paint processing, the properties of the coating material and of the object to be coated are known and also if all the quality-shaping variables within the range of economic and environmental requirements are addressed.

1.2 Retrospective

The aim of the following retrospective of materials and painting methods in the past is to highlight the entangled paths which coating technology has taken down to the present day by illustrating a few key events that will make its progress more transparent.

The early coating materials were natural resins . Dioscorides and Plinius report, among other things, on the use of countless exotic natural resins from the time of the Ancient Greeks and Romans. Later papers describe the importance of colophony, copals, shellac and dammar. Later still, in the 12th century, come reports of the combination of hardened natural resins such as amber with resinifying, i.e. chemically hardening, natural oils [1.3.6].

The application methods up to that point consisted solely of brushing or wiping techniques, without the generation of significant emissions, waste water or paint waste.

Rodgerus von Helmarshausen, also known as Theophilus, describes how to make coatings and provides a detailed recipe In chapter 21 of his book Schedula Diversarium Artium, which dates from around 1000 AD:

1* Put linseed oil into a small pot and add the gum which is called fornis

1* Place together four stones … place a common pot upon them and put into it the above mentioned gum fornis”, which in Latin is called “glassa”

2* Then place fire carefully underneath until this gum liquefy.

3* Have also a third pot nigh, placed upon the coals, in which is hot linseed oil

4* Pour the warm oil into it and stir it with the iron …

5* And take care in this, that in weight there are two parts of oil and the third part of gum…

Figure 1.2.1: First recipe of a coatings material by Theophilius

Around the end of the first millennium, the monk Rodgerus of Helmarshausen reports in his book Schedula Diversarium Artium the first details of the composition and manufacture of the then standard paint [1.3.7]. He is therefore, regarded as the creator of the first binding paint formulation and of the detailed instructions on how to make it.

Linseed oil and amber (called “rubber” in German back then), are boiled together in a ratio of 2:1, with the hardened resin acting as a nonvolatile film former, and the linseed oil as a chemically crosslinking reactive thinner. Solvents to regulate viscosity were not used at that time because they were not available in sufficient quantities.

In the 10th century it was the Arabs in the guise of the doctor Abu Mansur who taught the Europeans the art of distillation [1.3.8]. This art was then used in Europe for, among other things, extracting turpentine oil. When the van Eyck brothers took Rodgerus of Helmarshausen’s formulation, which was the first to be systematically described, and extended it by adding turpentine oil in the early 15th century, physical drying and thus emissions had been invented [1.3.9]. This outcome is noteworthy on one hand because it greatly expanded the use of painting and on the other because the associated environmental problems are still tying up a considerable part of paint-specific research capacity to this day.

The memorable “invention” of emissions was followed very much later by the “invention” of waste. By this is meant the introduction of the continuous production line by Henry Ford in the early 20th century and consequently the start of industrial-scale painting technology.

The production line has brought the world huge benefits in terms of speedy and economical production systems. However, the necessary faster coating processes could only be fully exploited by employing quick-drying paints and a new application method. Consequently, the oil paints which took several weeks to cure were superseded by quick-drying cellulose paints with solvent contents of up to 80 %. At the same time the waste-free brush method which had been standard up to that point was replaced by the spray method. However, the introduction of the spray gun, which had been invented by de Vilbiss back in the 19th century, also ushered in a new problem because it had an extremely poor material application efficiency of less than 50 %: the generation of paint waste and, at the same time, a dramatic increase in organic emissions because of the considerably higher solvent contents of the cellulose paints.

So, 1920 introduced a completely new situation into coating technology, but failed to provide an appropriate approach for the new problem. This approach had to be developed in the course of the following decades. The production line meant technical progress in the form of increased coating quality as a result of improved application and a more economical production system, though at the expense of the environment in the form of waste and emissions.