Chapter 1. Introduction to Colorants

Transcription

1 rigins of color Chapter 1. Introduction to Colorants - The most common mechanism of creating color is the selective absorption of light wavelengths, occurring in most dyes or pigments used in creating surface colors. - Examples of the use of light absorption in creating color might be dyed fabrics, paint layers, pigmented plastics or printed card. Light source Absorbed light by object Eye perception 1 2 rigins of color The fifteen causes of color Classification of colorants : or Pigment Dye - The Society of Dyers and Colourist (SDC) define a dye as: - Usually organic compounds - A dye exist in solution during part of the coloration process. - Dyes are generally used in the coloration of textiles, although other substrates such as paper and leather may also be dyed. 3 4

2 Classification of colorants : Dye or Pigment Pigment - The Color Pigments Manufacturers (CPMA) has defined pigments as : - Usually inorganic compounds, but some are organic compounds - Pigments are usually dispersed in vehicles or substrates for application, as for instance in the manufacture of inks, paints, plastics, or other polymeric materials Classification of colorants : Dye or Pigment Dyes and Pigments - These definitions classify the material according to how the material is used. - This is absolutely correct, as the same chemical compound can be used as a pigment or as a vat dye; it is the application process that determines whether the colorant is a dye or pigment - There are about 5,000 compounds classified as dyes in the Colour Index and about 400 compounds classified as pigments - Pigments retain a crystal or particulate structure throughout the coloration process 5 6 Brief istory of Synthetic Colorants After the Industrial Revolution Synthetic pigments 1704 Prussian blue Followed rapidly by Synthetic ultramarine Cobalt blue Cadmium reds and yellows Chrome oxide green (Army green) Synthetic dyes 1856 Mauve of Mauvine Followed by 2 Synthetic Indigo Synthetic azo dyes in every color imaginable Classification of colorants : Dye or Pigment Colour Index : omenclature - In 1920 the UK Dyer s Company (now transformed into the SDC) began devising some means or other to systematize the nomenclature of the colors - Plans for the Colour Index were announced in 1921 and by 1924 the first volume had been produced. - The Colour Index has been updated many times and, when the second edition was published in 1956, became the standard reference work for the listing and classification of colorants. 7 8

3 Classification of colorants : Dye or Pigment Colour Index : omenclature Classification of colorants : Dye or Pigment Colour Index - The aims of colorant classification system is to allow clear identification and description of colorants to aid people wishing to select and use colorants. - Each colorant is assigned a C.I. Generic ame and a Chemical Constitution umber - Generic ame : gives the nature of the product, the color and a chronological number - Chemical Constitution umber : A five-figured number that is assigned to a colorant depending on its chemical structure. Constitution number C Artists Palettes Through the Ages Red Yellow Green Blue White Black Pigments -- insoluble colorants usually inorganic compounds Cave painting 10,000 BC Egypt 1300 BC chre Fe 2 3 Red lead Pb 3 4 chre Fe 2 3 rpiment As 2 S 3 Malachite CuC 3. Cu() 2 Chalk (CaC 3 ) Gypsum (CaS 4 ) Egyptian Blue Chalk (CaC 3 ) CaCuSi 4 10 Gypsum (CaS 4 ) Malachite and azurite copper Cu Vermilion mercury g Prussian Blue, yellow ochre, red ochre, magnitite iron Fe Cobalt blue, cerulean blue cobalt Co Chrome oxide green, chrome yellow chromium Cr Pompeii AD 79 Renaissance 1400 AD Vermilion gs Vermilion gs rpiment As 2 S 3 Lead/Tin Yellow Malachite CuC 3. Cu() 2 Green Earth Complex iron silicate Egyptian Blue CaCuSi 4 10 Ultramarine Complex aluminosilicate Azurite 2CuC 3. Cu() 2 Lime Ca() 2 Lead White PbC 3. Pb() 2 Transition Metals 11 Impressionists 1860 AD Vermilion gs Chrome yellow PbCr 4 Viridian Cr 2 3 Cobalt Blue Co. Al 2 3 Lead White PbC 3. Pb() 2 12

4 Ideal Properties of Pigments Classification of Pigments Lightfast resists fading Chemically inert resists oxidation Insoluble as possible resists bleeding Good brightening or coloring power Uniform particles which can easily be dispersed in a binder igh opacity or hiding power Inorganic : the colored oxides, sulfides, hydroxides, sulfates, carbonates etc of metals. rganic : molecules based on primarily on aromatic carbons for backbone structure. - atural : minority group and used only for specialist applications. - Synthetic : commercially the most important pigments. The printing ink industry is by far the largest user of organic pigments (over 50% of the total production) The differences between rganic and Inorganic pigments The differences between rganic and Inorganic pigments Source : organic pigments are plants whereas inorganic pigments are manufactured from topical cosmetic and also from dirt Molecular Structure - Inorganic Pigments: the cations of metal are found in an array form with the non-metallic anions. This arrangement doesn't allow these pigments to dissolve in the solvent and plastic. Ex. Iron oxide yellow, black, red and tan pigments. -rganic Pigments: carbon chains or carbon rings are always present. sometimes in the molecules of the organic pigments, the atoms of nitrogen and sulphur atoms are also found along with the carbon atoms. ex. Azo, pythalocyanine, diazo and anthraquinone pigments

5 Dyes Examples of some common organic dyes Colorant which is homogeneously dispersed in the dye medium Usually soluble aturally occurring or synthetic organics Categorized by Method of Application 2. Chemical Structure a 3S 2 S 3a C 3 C 3 C 3 Chicago Sky Blue 6B (Direct Blue 1) 2 S 3a S 3a C 2 Disperse range 3 4-(4-nitrophenylazo)aniline 2 Ideal Properties of Dyes Lightfast resist fading Chemically inert Good brightening power Soluble as possible in order to apply Colorfast resists washing out of fibers 17-3S a +- 3 S C Lissamine Green B (Acid Green 50) C 3 C 3 a 3 S C 3 C 3 C 3C 2 Rhodamine 6G (Basic Red 1) methyl orange C 2C 3 Cl - C 2C 3 indigo 18 Uses of Dyes Coloring fibers and cloth Color photography Electronics dye lasers, solar cells, display panels Sources of atural Dyes BUGS Tyrian Purple or Royal Blue 9000 snails to obtain 1 g of dye Used primarily before 8th century A.D. to dye wool and silk Chemically it is 6,6 -dibromoindigo Biological and biochemical stains Foods and cosmetic Lakes used as pigments in modern paints Ink jet printer inks 19 Kermes the most ancient dye in Europe 70,000 female oak beetles produce 1 pound dye Cochineal Mexico and Central America Mexican cactus beetle 20

6 Kermes, Cochineal Carmine Sources of atural Dyes PLATS Indigo used since 2000 B.C. Extracted from Indigofera tinctoria avy Blue of English sailors Blue jeans Insoluble in water Must be chemical reduced to soluble leucoindigo to use as dye Chemically similar structure, light sensitive Dyed wool and silk carmine red 21 Woad (poor man s indigo) Member of the mustard family Common weed in temperate climates Leaves contain same chemical as indigo but in lower amounts Celtic war paint and tattoos Braveheart 22 Blue robes of priests Sources of atural Dyes PLATS Mauveine first synthetic dye Madder Turkey Red Root of madder plant found in Europe and Asia Prepared as a lake with Al() 3 British Redcoats Alexander the Great used it to simulate blood 2 Alizarin Synthetic alizarin prepared in 1875 William enry Perkin (18 years old), Trying to make the antimalarial, quinine - patent dye company 3 C 23 Quinine 24

7 Color Centers in rganic Dyes CRMPRES color bearer structural part of colored molecule which is responsible for its color Conjugated double bond systems Aromatic rings Azo groups yl groups Quinoid rings = C= AUXCRMES color augmenting groups functional group with non-bonded electrons which acts to strengthen or deepen the color and hue 2 R Common chemical classes of organic dyes AZ Dyes First prepared in 1863 ave widest range of colors of all dyes Contain the AZ Chromophore Generally lightfast Brilliant colors ranging from reds to blues R = R Azo group a 3 S range II C 3 a 3 S a 3 S 27 FD&C Red o. 40 Allura Red S 3 a FD&C Red o. 6 Sunset Yellow S 3 a 28

8 Anthroquinone Dyes Contain several C = groups Multiple aromatic rings riginate from plants & animals CARBYL Dyes Coloring agents in flowers, fruits, vegetables, bugs, etc. Methods of Application Dye and Substrate can interact through ionic forces (+ and charges) 2. hydrogen bonding 3. dispersion forces 4. covalent bonds C 2 C 2 Dye Substrate Alizarin C 2 Kermes C 2 Cochineal Types of Dyes by Application Acid or Basic Dyes (ionic forces) Mordant Dyes (ionic) Direct Dyes (hydrogen bonding) Vat Dyes Fiber-reactive Dyes (covalent) 31