Pigment

Pigments (Latin pigmentum for " color ", " make-up " ) are coloring substances, unlike dyes are insoluble in the application medium. Application medium denotes the material into which the pigment is incorporated, for example in paint or plastics. The generic term for dyes and pigments colorants, they may be colored or non-colored according to the chemical structure of inorganic or organic, and in accordance with the color impression. In biology, the term refers to all pigment coloring in a living organism substances. Technically, this is a colorant.

Decisive for the properties of the pigments, in addition to the chemical structure and the solid state properties such as crystal structure, crystal modification, particle size and particle size distribution, and the latter by the specific surface area. The color stimulus is produced by self- absorption and reflectance ( scattering or reflection ) of certain frequencies of visible light.

Pigments are incorporated in paints, emulsion paints, printing inks or as a coating pigment ( white pigments ) and filler in the manufacture and finishing of paper. In the coloring of plastics they are employed as well as for artists' paints and crayons. Other applications exist in printing on textiles or for coloring cosmetics and candles.

• 4.1 Classification in natural and synthetic pigments
• 4.2 Classification by chemical classes
• 4.3 properties
• 4.4 Industrial use

• 5.1 Natural organic pigments
• 5.2 Synthetic Organic Pigments 5.2.1 azo
• 5.2.2 Polycyclic Pigments
• 5.2.3 Other groups

• 6.1 metallic effect pigments
• 6.2 pearlescent pigments
• 6.3 Fluorescent Pigments

History

In ancient times, the technique of pigment processing was applied varied. Were found particularly in the ceramic, pigments black pigments (iron oxide black, manganese black ) that emerged from clays and ochres in the ceramic firing at temperatures around 1000 ° C. Great importance was carbon black, which was deposited over Rauchungsverfahren on the ceramic vessel bodies. Red pigments based primarily on the iron oxide red, obtained by calcination of ocher or iron-containing clays. Colloidally copper, which was taken at reducing burning of basic copper carbonates ( malachite, azurite ), was suitable for reds. For white pigments standing next calcium carbonate and kaolinite are available.

Cold processed pigments for wall, stone and wood painting are also based on ochres and clays ( black and red pigments ). Green pigments based on copper compounds, such as basic copper carbonate and Kupferhydroxychloriden that caused by immersion of copper sheets in salt solutions. Because of the clear hue was the " Egyptian blue ," a copper calcium silicate, desires, which was presumably produced through the melting of basic copper carbonate, calcium carbonate and silica sand. Also a long time as a blue pigment of the Cobaltaluminatblau was used, which was only rediscovered in 1804 as Thenards blue.

In the later painting a long time white lead was (Pb (OH) 2 · 2 PbCO3 ) the only available white pigment. From the beginning of the 19th century this because of its toxicity by zinc white (ZnO ) has been replaced. Today, the developed until the 20th century titanium white (TiO2 ) is used almost exclusively.

One of the most expensive colors until the 18th century, Blue, for which there was previously next to the Smaltepigmenten synthetically produced only the rare gemstone lapis lazuli as raw material, the latter gives, after an intensive process in the ultramarine blue.

The first industrially produced inorganic pigment Prussian blue was in the year 1704. The first organic pigment, Para Red, today CI Pigment Red 1, an azo pigment of β -naphthol group followed in 1885. Quinacridone copper followed in 1935 and 1955. Discovered in 1986, the chemical group diketo- pyrrolo - pyrrole pigment was the last guy who was able to gain significant market share.

Today pigments are used in many industries: paints, varnishes, printing inks and plastics, but also cosmetics, paper, building materials, ceramics and glass. In the textile industry are increasingly soluble dyes pigments, referred to therein as disperse dyes replaced. In 2006, the worldwide market for inorganic, organic and special pigments reached a volume of around 7.4 million tonnes. Accounts for the greatest share of Asia, followed by Europe and North America. In this case, sales of about 17.6 billion U.S. dollars (about 13 billion euros ) was achieved. In 2009, pigments have been sold worldwide for around 20.5 billion U.S. dollars, about 1.5-2 % more than the year before. 2010 sales of about 24.5 billion and 2018 around 27.5 billion U.S. dollars will reach.

Processing

Pigments typically arise in the form of primary particles. The primary particles can grow together on their surfaces to form aggregates. Of agglomerates occurs when primary particles and / or aggregates are connected by their corners / edges. Due to the dispersion process (dispersion ) during incorporation of the pigments into an application medium the pigment agglomerates are crushed. It creates smaller agglomerates, aggregates and primary particles. These are provided so as to be wetted by a dispersing medium. They should ideally be randomly distributed over the application medium.

In solid form, the pigment may be used pure (primary pigment), as a solid mixture of two or more pigments, or as a mixture with one or more fillers. By mixing with fillers, the color strength is reduced, whereby small quantities can be metered more. This possibility is used in powder coatings. Due to proximity effect primary pigments intense (simultaneous contrast).

For liquid coatings often ( prepared ) pigment preparations are used which contain either binder or binder-free. These pigment preparations are formulated as the paint itself, pre-dispersed pigment they contain high concentrations depending on the area in additives, solvents, water or binder. Advantage of the pigment preparations, the incorporation of a simple and exact, because the pigment is already dispersed and standardized. Disadvantage additives may act as the pigment preparation may not be more compatible with all paint systems.

(Usually 12-20 ) As Tönsystem (English Tinting system) the combination of several is pigment preparations, an automatic dosing system and a Rezeptiersoftware called. This method is used in architectural paints use. Pigment preparations may be mixed with other pigments or fillers. In addition to the commonly used liquid pigment preparations granulated, made ​​with readily soluble binders preparations are available if additional solvents are undesirable in the coating formulation.

A third, particularly in the plastics industry, widespread possibility is the use of solid pigment preparations, the so-called masterbatches. The pigments are einextrudiert or kneaded at elevated processing temperature in a binder matrix. After cooling, the solid again masterbatches are usually granulated, so that they produce more accurate and more reproducible colors when incorporated into the plastic. Also masterbatches can contain, depending on the desired effect, more pigments or fillers.

Nomenclature

Pigments are usually named with trivial names, trade names or names of the Colour Index (CI Generic Name ), since systematic nomenclatures lead according to IUPAC ( International Union of Pure and Applied Chemistry ) or CAS ( Chemical Abstracts Service ) to unwieldy name.

An example of

• Trivial Name: Brilliant Yellow
• Trade names: Aureolin benzimidazolone yellow
• Protected trade name: Hostaperm (TM ) Yellow H4G
• CI Generic Name: CI Pigment Yellow 151
• IUPAC name: 2 - [ [1 - [[( 2,3-dihydro -2-oxo -1H- benzimidazol- 5-yl) amino] carbonyl ]-2- oxopropyl ] azo] -benzoic acid
• CAS Index Name: Benzoic acid, 2 - [[ 1 - [[ (2,3- dihydro -2-oxo -1H- benzimidazol- 5-yl) amino] carbonyl ]-2- oxopropyl ] azo] -

View the properties

Pigments with common properties are grouped together, the results depending on the application to different subdivisions. DIN 55943 colorant initially divided into organic and inorganic colorants. Each group is divided into dyes and pigments. In the next level, the classification follows the optical effect. There is a distinction between dyes and white pigments, colored pigments and dyes, black pigments and dyes, effect pigments and fluorescent pigments. White dyes and the groups effect dyes are physically not possible since the effect as a pigment only to scattering ( white pigments ) or reflection ( effect pigments ) based. This requires an interface that does not have dissolved dyes.

The inorganic colorants are not divided as there is a standard from the coating area, and there is no inorganic coloring agent be used.

An ordered by hue listing individual pigments is given below list of pigments.

Inorganic pigments

Division into natural and synthetic pigments

The inorganic pigments distinction is made between natural and synthetic pigments. To the first group belong the earth and minerals ( earth colors, Mineral White ), which require for their application no or only a mechanical treatment ( mostly drying and grinding ). The second group includes inorganic pigments such as metal effect pigments, carbon black, white pigments, iron oxide pigments or zirconium silicates, ie synthesis products from different manufacturing processes. Synthetic inorganic pigments are used industrially because of stable quality and high purity produced today.

Not in every case it is necessary to choose the division or can be on the material to determine whether it is natural or synthetic origin. Such subdivision is difficult with iron oxide-containing paint layers of prehistoric painting. The specification cinnabar, the red modification of mercury sulfide, says nothing about a natural origin. Moreover, it was " vermilion " in ancient times, a synonym for all red and so synonymous with the red lead, the minium. The breakdown of the inorganic pigments in natural and artificial only came on in the 1940s and says nothing about the chemical structure.

Classification by chemical classes

Chemically, the industrially important pigments are divided into eight classes of substances. Specifically, these are titanium dioxide, carbon black, Bismutpigmente, oxides, hydroxides, Eisencyanblau, ultramarine, cadmium pigments and chromate.

The group of oxides and hydroxides is further divided into iron oxide pigments, chromium oxide and Mischphasenoxidpigmente as Rinmans Green, (the latter with the subgroups Spinel, hematite pigments, spinel pigments and inverse Rutilderivate ). The group of chromate pigment can be further divided into chrome yellow, chrome green and molybdates.

Soot here occupies a special position. Soot is inorganic by definition. It is often classified as an organic pigment because of the small particle size and the resulting performance properties.

Properties

Most inorganic pigments are distinguished in that they do not chemically react with the oxygen in the air, therefore are extremely resistant to aging and maintain their color virtually any length, but these by the aging of an organic Malmittels, such as oil, with time may be reduced.

Its high heat resistance makes use in porcelain painting possible. Only inorganic pigments can be used, since organic pigments are not temperature- stable and destroyed by burning. In industrial applications, high heat resistance for coloring plastics, powder coatings or coil coating is important, with heat-resistant organic pigments can be used because of the lower temperatures.

Earlier, nowadays rarely used, at least in Europe pigments such as cadmium sulfide, lead chromate molybdate or are harmful to health because it is heavy metal compounds.

The hue inorganic colored pigments is often described as dull compared to organic pigments. For pigments such as iron oxide pigments or chrome oxide green, this applies to full, but there are also some inorganic pigments with a pure tone. Of the pigments used in industry today this is essentially bismuth vanadate, but also the now discredited pigments cadmium sulfide, lead chromate molybdate or show a brilliant hue combined with good opacity. There are also comparatively rarely used pigments such as cobalt blue or ultramarine.

Industrial use

Because of their industrial importance and spread the white pigments occupy a special position. Alone in the paper industry well over 10 million tons per year are used in Europe, where the White minerals with calcium carbonate have by far the largest share.

In the paint area white is of paramount importance. In emulsion paints, it is the base color for Tönsysteme and beyond the main color. By value and production volume with about 60 % of all titanium dioxide pigments has the largest share. Worldwide 2006, almost 4.5 million tonnes of titanium dioxide were used. This position has reached in the course of the 1960s, the white pigment. Titanium White repressed due to its fastness white lead, comes to a strong increase in the total amount used in the industrialized countries. The easily accessible iron oxide pigments follow the value by 8% and by production volume by 22 % at rank 2 in the world pigment production, followed by carbon black in terms of value with 9 % and 4 % of the amount. The other inorganic and organic pigments are divided into the remaining amount. Due to the much higher price level, however, this almost 30 % can be achieved by value.

Among other inorganic pigments, in particular chromium (III ) oxide, ultramarine, bismuth vanadate, zirconium silicates, and the group of Mischphasenoxidpigmente are significant. Calcium carbonate is preferably used because of its refractive index in the paint industry as a pigment is not, but as a filler.

Organic pigments

Natural organic pigments

Organic pigments are found in nature as " animal " or " vegetable dyes " before. Some of these pigments can be prepared easily. Sootblack is an incompletely burnt wine wood. Some historically important pigments, such as the intensely colored Indian yellow from the urine of cows that lost exclusivity in the wide range of synthetic pigments. The soluble, almost colorless leuco form of indigo, the leuco indigo or indigo white is by oxidation with atmospheric oxygen to insoluble colored pigment indigo.

Synthetic Organic Pigments

Synthetic organic pigments are classified according to their chemical structure. The most diverse and largest group are the azo pigments. These pigments account for over 50 % of the amount of organic pigments sold. The other group is summarized to the polycyclic pigments or colloquially Nichtazopigmenten.

Azo pigments

Azo pigments are pigments whose property essentially emanates as a chromophore by the delocalization of electrons from an azo group (-N = N- ). Azo pigments are therefore, contain at least one azo group. The azo pigments can be further divided into classes, the chemistry allows a rough indication about the authenticity of the pigments. The actual authenticity depends largely on the substituents used, but also on the particle size. A distinction is made according to the number of contained azo bonds between monoazo and common pigments. It is further distinguished by the respective substituents.

The monoazo pigments include the simple monoazo pigments, such as the β -naphthol pigments and naphthol AS pigments and the laked azo dyes. Some of the most important organic pigments used today belong to this group, at the same time it is the oldest industrially available group. Examples are C. I. Pigment Yellow 1, 3 and 74, C.I. Pigment Orange 5 or C. I. Pigment Red 112

A special case are the benzimidazolone, which in turn are monoazo pigments and possess polycyclic substituents. This lead to a very good weather resistance, so that these pigments to achieve the highest fastness within the azo pigments. Examples are C. I. Pigment Yellow 154 or C. I. Pigment Orange 36 The disazo pigments include Diarylgelb pigments ( CI Pigment Yellow 83), the disazo condensation pigment (CI Pigment Yellow 128) or acetoacetanilide - pigments ( CI Pigment Yellow 155). Azo metal complex pigments are a special case, strictly speaking, because they contain no real azo group.

Laked pigments, so convicted with metals in salts, originally soluble dyes found in textile dyeing application. Color lakes means that soluble dyes are fixed as ( coloring ) on the fiber by reaction with metal salts or tannin.

Polycyclic pigments

Polycyclic pigments are compounds in which the property is produced as a chromophore by a delocalization of electrons across a more or less extended ring system.

The main share of polycyclic pigments provide the copper phthalocyanine pigments, which make up about half of polycyclic pigments. The main representatives of this group are the different types of Phthalocyaninblaus and the halogenated types ( Phthalocyanine ). Other important polycyclic pigment classes are Quinacridones, Diketopyrrolopyrrole pigments, dioxazines, perylene, and isoindolines Inthanthrone.

Other groups

In addition to these two substance groups still exist a number of organic pigments of different composition. They often possess a particular application. For economic considerations or requirements on the authenticity only a chemical compound of this structure is often suitable as a pigment. Representatives of this group are laked dyes which have the form of salts of heavy metals lost their solubility and thus are pigments.

Properties

Organic pigments are distinguished from inorganic pigments, mostly due to the higher color strength, the lower opacity, higher chroma ( chroma) and lower resistance to weathering. In addition, organic pigments are often more expensive. Organic pigments are treated to enhance certain performance properties such as dispersibility or covering power. Due to the post-treatment also the particle size is adjusted, which is responsible for fastness, color strength and to fine tune the color properties.

Toxicology

With regard to the toxicology of organic pigments is generally accepted that these pigments are in themselves due to their low solubility physiologically inert. Health concerns arise as a fine dust. Organic pigments are practically not biodegradable. Since pigments are used in the intermediate or end product using dispersants, binders, solvents and the like, where applicable, the toxicological effects of these substances to be tested.

Toxicological concern degradation products of pigments may be, these occur when irradiated with laser light on how to remove pigments of tattoos. In the cleavage of the tattoo pigment C. I. Pigment Red 22, produced by laser light, the 2- methyl-5 -nitroaniline and toxic krebseregende.

Demarcation

• Acid -base indicators are not among the pigments: There are dyes that change color with the pH of the solution

• Substrate color consists of a shade -providing component and a more or less colorless pigment, the substrate. Both components are bound in a conversion process water and bindemittelunlöslich together. In antiquity and the Middle Ages mostly vegetable dyes ( dye plant ) were mounted on a white substrate such as chalk or white lead; this mordants such as alum and soda were added, which improved the connection between dye and substrate.

Effect pigments

Metallic effect pigments

Brass, and aluminum are the principal pigments for producing a metal effect. Colors obtained by brass particles have a golden appearance, while aluminum creates a silvery in matching platelet shape. Previously used descriptions are silver bronze for aluminum pigments and depending on color and alloy bronze gold, pale gold, rich pale gold and rich gold brass pigments.

The visual impression is angle-dependent. In the top view ( almost perpendicular ) is the seemingly brighter metallic effect pigment while seeing emerges at a shallow angle of the mostly dark set base color. This effect by the platelet-like shape of the particles is called the flop. Aluminum flake pigment in a suitable particle size result in silver luster, nearly spherical particles of the same particle size form a uniform gray surface. Since untreated aluminum pigments are only moderately stable in aqueous systems and in particular under Bewitterungseinfluss, surface-treated marks were developed to compensate for this disadvantage.

The color depth is related to the grain size in relationship. The exact appearance of the pigment is mainly determined by the particle size and the regularity of the particle. Coarse particles thereby produce a sparkling impression, which is called Sparkle. Finely divided particles produce a smoother flop, so a smoother transition when changing the viewing angle. To achieve the desired effect, both types are also often used.

Pearlescent pigments

These pigments are referred to as interference pigments. They consist of plate-like carrier substrates with low refractive index, usually natural mica, silica, or very thin glass plates that are coated with one or more extremely thin and very uniform oxide layers of high refractive index. Are preferably titanium dioxide, iron ( III) oxide or zirconia, mixed oxides of the said compounds are used. As the coating method, the sol-gel, CVD or PVD method are used mainly. The layer thicknesses produced are in the range of 100 nm In the preparation of a precise control of the coating thickness is critical ( ± 3 nm ) and their homogeneity.

The choice of coating parameters, primarily refractive index, film thickness and layer sequence, almost any colors and shades can be realized by the effect of interference. Under certain conditions, viewing angle-dependent color-flop colors can be produced in which the hue changes depending on the viewing angle of the observer.

Pearlescent pigments are by their construction health risk and approved by the FDA for coloring food.

Fluorescent Pigments

Luminescent pigments are on the one hand intensely colored fluorescent pigments for fluorescent colors ( " Neon " ) and on the other hand, photoluminescent phosphorescent materials. They are used in so-called Leuchtfärbemittelnn. Usually consist of incorporated into a matrix fluorescent dyes fluorescent pigments, the pigment thus obtained properties. As Afterglow doped inorganic materials are used with phosphorescence. Spread the green fluorescent pigments zinc sulfide-based are the same as escape routes are marked.

The radioactive bulbs are not counted to the pigments, although they are insoluble. There are self-luminous radiation which takes place not by UV or sunlight, but by radioactive excitation.

Standardize

• EN ISO 4618 Paints and varnishes: Definitions
• DIN 55943 colorants: Definitions
• DIN 55944 colorants: Classification according to coloristic and chemical aspects