Dyeing Process and Properties PDF

# Jay Bayarangbalil ## What is dye? Explain Dye is an aromatic hydrocarbon capable to impart color to the substrate (paper, cloth, leather, food etc). In a considerable fashion, it can change properties of material. ### Characteristics/Requisites of A True Dye - It should be soluble in almost all solvents. - It should give good dispersion in solvent. - It should have sharp and intense color. - It must be non-toxic. - It should be soluble in water. ## Explain relation between colour observed and colour seen! | Tmax (nm) | Absorbed | Seen | |------------|------------|--------------------| | 400 - 435 | Violet | Yellow - Green | | 435 - 480 | Blue | Yellow | | 500 - 560 | Green | Purple | | 560 - 580 | Yellow - Green | Violet | | 580 - 595 | Yellow | Blue | | 595 - 605 | Orange | Green - Blue | | 605 - 750 | Red | Blue - Green | - The table shows wavelength range of the component of visible part of radiation. When any component absorbed in visible part of the spectrum, it appears color to the component. - The light either reflected or transmitted by the component produces cyclical/psychological sensation of color. - Thus color seen is complimentary to that which is absorbed by a compound. For example, when 450 mm light is absorbed, yellow color is seen. Therefore Yellow and Blue are said to be complimentary color because absorption of one form produces the other. - Only green leaves absorbed in the real region. - When all radiation absorbed, black shade is obtained while all radiation reflects, white shade is obtained. - Absorption in a narrow region gives brilliant shade while wide range of absorption produces dull shade. ## Explain chromophore - oxochrome - the dye - Witt proposed a dye molecule is made up of two parts, chromophore and oxochrome. The Greek letters mean color. Phoros means bearing. - Certain unsaturated groups are present in any organic compound impart color to that compound. Such color bearing group is known as chromophore. Some important chromophore are as follows: 1. -NO2 (Nitro) 2. -NO (Nitroso) 3. -N = N - (Azo) 4. -N = N - O (Azoxy) 5. -N = N - NH (Azoamino) 6. === (p-quinomonid) 7. (o-quinomonid) 8. -C - (Carbonyl) 9. -C=C- (ethylenic) 10. -C - (Thiocarbonyl) S - The first seven are independent chromophore because a single group is sufficient to impart color to the compound. - The last three are dependent chromophores because a single group cannot impart color. For example, CH3 -f-CH3 is colorless whereas 2,3 -butadiene is pale yellow. - The proximity of such dependent chromophores also influences the color. For example, H3C -f-CH2-CH2-f-CH3 is colorless. - Chromogens are compounds which contain chromophore, but they don’t represent dye without the presence of auxochrome. - Greek letters, Dauxin to increase, and chromo, means color, makes the word oxo-chrome. - Oxo-chromes are certain groups which do not impart color to a molecule but are responsible for deepening of color. - Some typical oxochromes are: -NH2, -NHCH3, -NR2, -CH3, -OCH3, -COCH3, -CN, -OH, -CONH2. - For example, Benzene is colorless but Nitrobenzene is yellow and p-nitroaniline is dark yellow in color - Mittki's theory stated that the color of dye is deepening by addition of substituents such as methyl, ethyl, thenyl to increase the molecular cut of parent dye. Yellow azo dyes from benzene turns red when Naphthalene is substituted for benzene. - Armstrong’s theory stated that all color compound could be represented by quinonoid str. If such a str should not be assigned a compound it would be colorless but imino quinone (HN = NH) is colorless while C6H5-f-f-C6H5 is pale yellow. - In 1907, Bayer observed that the color might be due to structural oscillation of quinonoid condition between two benzene ring. Image showing the chemical reaction of amination converting Fuchsohimme (colorless) into Doebner's Violet. ## Write note on MO theory In a molecule, the shifting of one electron from lower energy state to that of higher energy state is called molecular excitation. Various transitions may be arranged in increasing order of energy as: * $σ < π < π* < n < σ*$ NCC3H3, CH2 = CH2 → 227 mm, 171 mm - *σ* to *σ* transitions require very large amount of energy. The compounds like saturated hydrocarbon may undergo *σ → σ* transitions - The energy requires for *n → π* is much lower than *n → σ* hence, the compounds having non-bonding electrons usually absorb in ordinary region. - The *n → π* and *π → π* transitions are at lower energy than *n → σ* and s → s* therefore absorbance takes place at longer λ. - Conjugation of double bond, decreases the energy required for *π → π* transition and absorption is shifted to longer λ, For example: * Ethylene (171 mm) * Butadiene (217 mm) * β-Carotene (451 mm) ## Write a note on Valence Bond theory - This theory depends upon following postulates and is known as resonance theory. Chromophores produces color because their π-electrons get excited by the absorption in visible region. - Oxochromes increase resonance by the interaction of their unshared pairs of electrons with π-ces of the aromatic ring. Increase in resonance deepens the color. - The dipole moment is related with the oscillation of electron pairs in the molecule. Increase of excitation of some group is: - NO2 > CS > -N=N- > -CO > -CN > -C=C- * Easier, the excitation deeper will be color. * As the number of changed canonical forms increase, the color of compound deepens. Hence, the possibility of oscillation for a change is longer in the compound thus the symmetry of molecule is related with the color. - Bury suggested that the shifting of ionic change is only necessary to give rise to two different structures. For example, Doebner’s Violet gives nine intermediate structure between two extreme structures given as: Image showing the chemical structure of two resonance structures, A and B, of Doebner's Violet. All nine contributing structures constitute different energy levels and has a concept of resonance. The energy levels are high enough to jump a large energy from one to another so it travels through the conjugated chain from one atom to another. Thus, a series of intermediate structures are produced. - The structures (A) and (B) are higher in energy because they are positively charged and either one and or two lesser no. of π bonds than (A) & (B). ## Explain p-nitrophenol is colourless but yellow in alkaline soln? Image showing the conversion of p-nitrophenol to p-nitrophenox-ide in an alkaline solution. - In alkaline soln. p-nitrophenol exist as p-nitro phenoxide ion. Therefore the changing structures are contributing to resonance. So the compound absorbs light of a longer wavelength and hence appears yellow. - Nitrobenzene shows the charged structure which contributes to resonance hybrid but it contributes very little to either GS or ES. Therefore Benzene absorbed in UV region while nitrobenzene absorbed much more than that of benzene. ## Explain effect of conjugation on color - The longer conjugation, provides longer π path for resonance and saw the color will be more deeper. Examples showing the conjugation of: * Benzene * Naphthalene * Anthracene * Naphthacene * Pentacene Image showing the chemical structures of Benzene, Naphthalene, Anthracene, Naphthacene, Pentacene and graphite. - The number of fused rings increases, the color deeper more and more. Benzene, Naphthalene, Anthracene are colorless while graphite is black. - The conjugated system having heteroatom absorbs the light of longer wavelength, then the corresponding compound containing carbon only. ## Explain Michler’s hydrol is colorless but its cation is blue. Image showing the structural formula of Michler's hydrol and the reaction of Michler's hydrol with an acid to form the blue cation. - Cation is planer and it is the resonance hybrid of two extreme structures differed in their electron distribution. The resonance is spread throughout the molecule which is responsible for the absorption in visible ray while in hydride form it is colorless because of the lack of co-planarity. ## Explain different types of forces, place role in dying process. - Dying is generally carried out in aqueous solutions. It is the process by which the color is transferred from the dye bath to the substrate being dyed. The attachment of the dye molecule to fiber (substrate) is adsorption process. The dye molecule may be bound to the fiber by involving either one or more types of forces from the following: 1. Ionic forces: - Ionic bond can be defined as electrostatic attraction called by atomic interaction which involves transfer of one or more atoms from one to another atom, like NaCl. - In case of dyeing, ionic bond arises from ionic sites of opposite charge. In the fiber, wool contains free amino acid groups, its dyeing is carried out in the presence of acid, like: Image showing the chemical reaction of an amine reacting with acid. - The dyeing of cellulose could not explain through hydrogen bonding because the amorphous region of cellulose have greater affinity for water molecules. Dye molecules are not capable to displace this water molecule. Cellulose dyeing is explained by co-valent bonding 2. H-bond: - The co-valent bond, hydrogen atom except electrons from the lone pair of electron donor atom, like N, O, F etc. present in a molecule. Therefore hydrogen bonding arises from electrostatic attraction between small positive charge on H atom and the unshared electrons on electronegative atom. It is believed to be ionic in nature and it is weak force, but several hydrogen bonds between dye and fiber may be sufficient enough strong then to hold dye on fabric. - For example: Image showing an example of a dye molecule interacting with a fiber through H-bonding. 3. Co-valent linkage: - It arises when two interacting atoms share their electrons mutually. There are actual chemical bonds between the dye and substrate molecule. They are formed by chemical reaction between, reactive dye, alcohol, hydroxyl group. In cotton fiber, this linkage has very high washing fastness. Image showing the chemical reaction of mercerization, and the subsequent reaction with dye molecule to covalently bind the dye to the fiber - Only one chlorine atom of dichlorotriazyny system undergoes reaction with cellulose (OH system) yielding different attachment, the other chlorine gets replaced by water. 4. Vander Vaal’s forces: - The interaction are weak and arises due to interaction in linear fashion. This force is effective only when dye molecule is long and flat. The dye and fiber, both need to contain alkyl or aryl group. The linear dye molecule can approach close enough to the fiber molecule. Image showing a generic representation of a dye interacting with a fiber through Van der Waal's forces: - Example: | Fiber | Dyes | |------------|-------------------------------------------------| | Cotton | Direct, Vat, Sulphur, Ingrain, Reactive, Azoic | | Wool | Acid, Acid-mordant, Basic, Disperse Blue Dye | | Polyester | Acid, Disperse, Dispens, Reactive | | Polyamide | Cationic, Disperse | | PAN | Cationic, Disperse | ## Explain basic operations in dyeing process - Dyeing process follows the following steps: 1. **Preparation of the fiber**: - The fiber must be secured with soap and other detergents before they are dyed because the raw material made gets associated with substances like sizing material, oil, wax, lubricants during spinning. 2. **Preparation of the dye bath**: - The dyeing bath is prepared by adding certain chemicals to the solution of water. Soluble dye, they are known as wettis agent, carriers, retarders etc. The carrier improves dyeing rates of hydrophobic fibers because they act as a swelling agent. - Retarders slow down the dyeing process at the desired level by competing with the dye to react with the fiber. Cry-COOH is used as a retarder. Then wool dyeing is done with acid dyes. - The insoluble vat dyes are reduced with alkaline hydrosulphite and in the vanishing, such sulfisel are subjected to air oxidation. 3. **Application of dye**: - The fiber are immersed in dye bath for a specified time at optimum temperature. Steaming is useful to obtain a uniform dye. The condition of dye requires time and depends upon the nature of the dye and absorptive power of the fiber. Dying can be achieved by hand operation or by machine, in hand operation. The substrate is moved in open vat containing the dye liquor. While machine dyeing is a continuous process. ## Explain different types of fastness of dyes 1. **Water fastness**: - This test determines the resistance of color of dyed textile to immersion of color dyed and undyed specimens are kept in intimate contact. Smell stench to gather them. They are immersed in water, drain and placed in Penspeedometer. It is apparatus which held the specimen under comparison between the glass kept vertically at 0.01 Pascal. The pressure is kept for some specified time. The pieces are separated, dried, and checked for staining on the undyed clothes using standard grey scale. 2. **Sublimation fastness**: - The specimen is prepared by some method described in water fastness but this test is mainly applied to hydrophobic fibers. 3. **Milling fastness**: - Milling is several mechanical washing applied to cool during manufacturing of alkaline milling a dyed specimen of wool is made into a small bag. The prepared sample is protected in washing wheel containing alkaline sol. The alkaline soap soln. is replaced by dil. H2SO4. 4. **Washing fastness**: - The dyed and undycel samples are stitched together and the specimen is poured in soap soln. for 30 min. Then rinse, dried and checked for staining. 5. **Perspiration fastness**: - The prepared specimen are immersed in soln. of Hisitiding by 0.5 hours and then after draining, the specimen are placed under comparison in Penspeedometer. 6. **Rubbing fastness**: - It is the resistance of dyed textile to rubbing of and staining of other materials. To check such fastnesses, a machine named Crock meter is used. 7. **Burnt/Gas fastness**: - This test referred to resistance of dye, hydrophobic fiber to the action of oxide of N2 in the chamber, the temperature must be maintained at 140 ℉. And on the basis of change of shade, the degree of staining can be fixed. 8. **Light fastness**: - It is accessed on a scale of 1 to 8. The light fastness is determined by the comparison of dying with standard. The scale: 1 - Least fastness, 8 - Best fastness. To check the fastness, sun test or ferrocolormeter test are carried out. ## Write a note on Textile Printing: - In Textile printing, methods like block printing, roller printing and screen-printing are used to create different designs. 1. **Block printing**: - The particular pattern in the design of carving is associated with wood by means of carrying. The block is furnished with colored inks in associated with the thickener, and other adhesive. The complete design can also be absorbed by appropriately counted, wooden blocks in sequence and in accurate registration. 2. **Roller printing**: - The stainless steel or copper rollers are engraved, with the design, on the same principle as for block. Each roller has its own color and proper combination of appropriate rollers forms complete design when used in sequence. 3. **Screen printing**: - The wooden frame is mounted by the silk fabric. The designed for a single color is transferred to silk screen by a photographic technique using bicromate and gelatin. One part of the screen corresponding to design consists of soluble gelatin and is removed by washing with water while the gelatin remains past of the screen is rendered insoluble by a photochemical process and the insoluble gelatin are required by the design plate. The past passes through the screen. ## Write classification of dye Dyes are classified according to: 1. **Chemical constitution**: - It is the symmetric treatment based on structural unit, their sub-division are made on the basis of various systems present in the molecule for example. - -N=N- (azo group) has subgroups like monoazo, diazo, triazo, tetraazo, stilben azo, pyrazolone azo etc. * **Nitroso dyes**: - HNO2 → Image of the chemical reaction of p-nitrosophenol. - It is a small group of less technical importance. Phenols and naphthols are easily nitrosated by the action of nitrous acid. Then quinone also formed. -*Nitroso compound* by reaction with hydroxyl amine, and are usefull to prepare indo-phenols, the turmeric oxime is greatly stabilized by H-bonding, the metallic derivative can be formed, with FeSO4. This lake is fast to light and washing, and is also known as fast green O, or Iron green lake. - For example: Image showing the chemical synthesis of fast green lake from p-nitrosophenol. * **Nitro dyes**- It has phenols, or amines containing Nitro group at ortho and or para position. The water soluble members are colors, and useful, for example: - Image of the chemical synthesis of Naphthol Yellows from 1-napthol-2,7-disulfonic acid. - It produces truple yellow shade on wool and silk * **Amide Yellow E**:- Image of the chemical synthesis of Amide Yellow E from chlorobenzene and the subsequent reaction with p-tollidene. * **Polar Yellow Brown**: Image showing the chemical synthesis of Polar Yellow Brown from a starting compound with an amine group. - It has very good light fastness than Amide Yellow E, and also better washing fastness, so in wood dyeing because of H-bonding two -SO3H group gives more ionic strength to the dye. * **Picric Acid**: - Image showing the chemical synthesis of Picric Acid from phenol. * **Azo dyes**: - It is the most important class of the dyes and it covers 50 % of commercial dyes. It contains at least one -N=N- group and it is attached to one or two radicals and generally, both are aromatic. Here, both the ene “N” shows the by sp3 hybridization and it remains trans to each other. - A indicates radical containing accepting group, and E indicates radical containing donating group. - The dye which contains only aromatic radicals are known as carbocyclic azo dyes but if they contain one or more heterocyclic radical then the dye are known as heterocyclic azo dyes. * **Orange I**: - Image showing the chemical reaction of the formation of Orange I from sodium naphthionate. * **Congo Red**: - H2N-(O) NH2 → Image showing the chemical synthesis of Congo Red from benzidine. * **Stilbene Azo**: - Image showing the chemical synthesis of Stilbene Azo from the starting compound with a nitro group - Tetraazotization of Stilbene diamine produces azo dyes on coupling with proper coupling it gives excellent fastness on wool. * **Pyrazolone Azo**: - Image showing the chemical synthesis of a Pyrazolone Azo dye from the starting compound with an amine group. * **Direct Black 38 (Direct Deep Black)**: - HON - (O)-(O) - NH2 → Image showing the chemical synthesis of Direct Black 38 from benzidine. * **Diphenyl Methane dyes**: - *Auramine O* is a basic dye having yellow shade. It has poor fastness. It gets hydrolyzed readily and forms colorless Michler’s ketone and ammonia. - Image showing the chemical reaction of the formation of Auramine O from Michler’s ketone * **Malachite Green**: - CHO + 2 Image showing the chemical synthesis of Malachite Green from benzaldehyde. - *Rosaniline dyes**: - CH3 + C6H5NH2 + FeCl3 → Image showing the chemical synthesis of Rosaniline dye from benzaldehyde. * **Aniline blue**: - CH3 + C6H5NH2 + Image showing the chemical synthesis of Aniline Blue from benzaldehyde. * **Crystal Violet**: Image showing the chemical synthesis of Crystal Violet from Michler's ketone. - The preparation of Crystal Violet gives information about oscillation of change, based on the solution used. - For weakly acidic solution, singly change dimensional oscillation is in horizontal direction. - For acidic soln., strong, it is doubly changed and whole unit undergo oscillation which depend the color. If the color is in a very strong acidic solution, it is triply charged, so little resonance is observed, which lightens the color. - It is useful for dyeing and printing, manufacturing of ink, copying pencils, typewritten readings, ribbons * **Methyl Violet**: Image showing the chemical synthesis of Methyl Violet from Michler's ketone. * **Xantheno dyes**: - It gives fluorescent base having red-to-yellow green color * **Fluorescene Dye**: Image showing the chemical synthesis of fluorescene dye from resorcinol. - Na-salt of fluorescene is known as uranine which is very useful in dyeing wool and silk. Fluorescent colour also used to trace under ground current in sea, and in rivers. * **Rhodamin B**: Image showing the chemical synthesis of rhodamin B from phthalic anhydride. * **Anthraquinone dyes** ([AQ]) * **Alizarine**: Image showing the chemical synthesis of Alizarine from anthraquinone. - Vat yellow-1 to Vat blue-4: Image showing the chemical reactions for synthesis of Vat yellow-1 and Vat blue-4. * **Acridine**: - This dyes have Acridine skeleton and amine and substituted amino group 9 to 6, or only at 9 to 6 position 3rd Phenyl ring may present. 9-Position in case of tri-phenyl methane derivative. Image showing the chemical reaction of acridine. * **Acriflavine**: Image showing the chemical synthesis of Acriflavine. * **Read: Taper dye (Safranmine T)**: Image showing the chemical synthesis of Safranmine T. * **Indigo dyes**: Image showing the chemical synthesis of Indigo. - *Vat blue 1*: - *Classification of dyes based on the mode of application*: 1. **Acid dyes**: - Na-salt of color acid having sulfinic and phenolic group. - Generally used for dyeing wool and silk, applied in acidic media for salt of acid. - For example, picric acid, martius acid, orange-1, orange-II, etc. 2. **Basic dyes**: - They are cationic dyes, generally hydrochloride and zinc chloride, complexed with color bases. - They are used for silk and cool. - Applied in basic media. - For example, methyl violet, crystal violet, methylene blue. 3. **Direct Substantitive dyes**: - They are salt of color acid and mostly are Azo dyes. They are used for cellulose because of good absorbant. 4. **Mordent and Adjective dyes**: - Applied for prior treatment of some mordent, like Alumine, chromium, iron. The nature of the mordent depends upon the nature of the dye. - *For basic dye*, acidic mordent like tannic acid is used. And *for acidic dye*, basic mordent like, salt of chromium, aluminum, iron etc. are used. 5. **Ingrain or Developed dye**: - This dyes are produced within the fiber. - Azoie dyes are called ice colours. For example, azo dyes in which, cloth is soaked in phenol or amine followed by diazonium salt solution. 6. **Vat dyes**: - These are insoluble in water or there reduced form soluble in water. - When these carbonyl groups are reduced in a soln. of caustic soda and NaSH they exhibit affinity form cellulose fibers. - For example, Image showing the chemical synthesis of the reduced form of Indigo. - Therefore, this dyes are applied in there reduced form *which are obtained, by reduction of compound, which some reducing agent like alkaline sodium hydrosulphite in a large woolen vat, giving rise to the name vat dyes*. - The cloth to be dye is immersed in the vat having a reduced vat dye. After the absorption of reduced dye, the original insoluble dye is reformed by oxidation with air. This chemically this process of dyeing is very fast to washing, like bleaching as well. - For example: Image showing the conversion of Indigo Blue to Indigo White. 7. **Sulphur dyes**: - These are insoluble dyes and when reduced with sodium sulfide they become soluble and exhibit affinity of Cellulose. - This dye is absorbed directly but upon exposure to air, they are reoxidized to their original insoluble form inside the fiber thus they become very resistant to remove by washing. - This dyes contain sulfur as a part of chromophore, as attached sulphide chain. The exact constitution of most sulfur dyes are unknown. - They have good fastness to washing, bleaching, perspiration, and wet fastness. - Its important weakness is the lack of fastness to chlorine drying dyeing. So it used mostly on cotton, silk and rayon. 8 **Disperse dyes**: - This dyes molecules are small and have some hydroxide, and some amino groups to give water solubility at dyeing temperature. - Generally this dyes are water insoluble color organic substances. - Originally introduced for dyeing cellulose acetate, and usually applied for fine dispersion. - They can be utilized for acetate, triacetate, nylon, polyester and acrylic fiber. - Disperse dyes are usually brown in a mill for finding particle size in an aqueous solution containing dispersing agent. It may applied by a dried heat to polyester fiber in this process, the dye may be achieved by sublimation from the solid dye to the fiber. Most Teflon fibers may be dyed under pressure or with the use of organic swelling agent. The washing fastness of dispersed dyes on this fiber is excellent. ## Non-Textile application of dyes - The main application of dyes is for coloring textile. - Dyes are also useful coloring a number of other substances such as leather, paper, food stuff, drugs, polymers, cosmetics, ink, lacquers, varnish, paints, shop, plastic etc. - Dyes can be dye with, Tropene substance, and can be dye, as acid dyes finish leather, also cam be, dye, with pigments. - When basic dyes are use for dyeing leather, they give tower full rich and full shade. - The main drawback of this dye, is that they are not fast to light when if saids are dye a reling of shade take place. - The dyes use for leather, may not have fastness property, but then, should not be highly sensitive to variation in the leather. - In some leather dyes, alkyl sulphonic groups are are present, and they improve the penetration. Image showing the chemical structure of a yellow dye. - Example: - *Moldolus blue* Image showing the chemical structure of Amido Naphthol Brown 3G. - *Amido Naphthol Brown 3G* - Image showing the chemical structure of a dye used to color the leather of gloves. - Modern dyes are becoming popular with glove tanners, and are dyed by metachrome method. ## Food colors - Food colour is mainly used for nutrition. If food is made more acceptable the color is used. Originally the substances used for coloration. There are matrunally colouring matters, like, chlorophyll, Cochinea, saffron, and turmeric. However, they are still used to a great extent these days synthetic dyes find. extensive use due to following reasons: 1. They offer a variety of shades. 2. They are cheap. 3. They can be handled easily. The criteria for selecting synthetic dyes for dyeing food are as follow: 1. They should be stable to light. 2. They should not be interact other ingridiant. 3. They should not interfere the test and the flavour of the food. 4. They must be made free from harmful constituents. 5. They must be totally harmless to human beings. - In order to achieve the above properties, the food colors are to be certified and permitted. - The dyes used for coloring foods are as follows: Image showing the chemical structure of (1) Orange-I, (2) Amaranth, (3) erythrosine, (4) fast red-TS. ## Ink dyes - Ink dye industry developed with development in writing, drawing and printing. - Early days, natural dyes were used for example, liquid from cuttlefish or mollusc. - **Ink formation** made up of iron salts of tannic and gallic acid *were found to have good fastness properties so they were used for official documents*. - **Ink dyes can be divided into two major parts**: 1. **Drawing, writing and marking**: - *Fountain pens*: Aqueous dye-link - *Ball point pen*: Combination of dye and pigment. - *Fluorescent marker pen*: Water soluble dyes used for highlighting text passages. 2. **Ink Jet printing**: - It is highly developing area now a days. - Ink droplet is injected from the nozzle, in a controlled manner and applied to the surface, to get different shades (paper, ceramics, glass, textiles, plastic etc.). **Properties of an effective aqueous dye for ink jet printing are**: 1. Good tinctorial strength. 2. High water solubility (5-20%). 3. High water fastness on substance. 4. Rapid fixation after deposition. 5. Good durability. 6. High chroma (color). 7. Good thermal fastness. 8. Low toxicity. - Ink formulation research aimed towards achieving the following print properties: 1. Good optical density. 2. No feathering. 3. Minimal black to color bleed. 4. Uniform and controlled drop spreading. 5. Good water fastness. 6. Rapid dry time. 7. Smear resistance. 8. Media Compatibility. - Examples: 1. **Black dyes**: For example, Direct black-2: Image showing the chemical structure of Direct Black-2. 2. **Color dyes**: For example, Magenta (purple-red): Image showing the chemical structure of Magenta. 3. **Direct Yellow 86**: Image showing the chemical structure of Direct yellow 86. * **Synthesis of inkjet dye 20**: Image showing the chemical synthesis of inkjet dye 20. ## Photographic dyes: - An ordinary photographic plate is sensitive to only violet or blue, and UV light. - If certain dyes are added to the photographic emulsion, then the plate becomes sensitive to the whole visible and near IR light. - All dyes, are not act as photographic sensitizers, if a complete sensitizing effect is to be observed, that dye must be pure and applied in very diluted form. - The discovery of color photography could be attributed to the synthesis of efficient sensitizing dyes. * **Cyanine dye**: - They are one of the oldest synthetic dyes. But the sensitizing properties were discovered later. The use of cyanine dyes *is a photographic sensitizer is limited because they causes fogging effect, on pictures.* >*The sensitizing efficiency of cyanine dyes can be enhanced by adding ammonium alkali, or various thiocyanate to the emulsion. The cyanine dyes contain two quinoline moiety linked through odd methine group (=CH-). It has two nitrogen auxochrome linked with odd numbers of sp2 hybridized carbons. The general form of cyanine dye: <*> - Cyanine dyes are subclassed based on: 1. No. of methine groups (=CH-) 2. Position of linkage (cyanoline) Image showing the general structural formula of a cyanine dye. - Examples: | Linkage | NO. OF =CH- | | |----------|----------------|------------| | 4, 4’ | =CH- | Cyanine | | 2, 4’ | =CH- | 150 Cyanine | | 2, 2 | =CH- | Pseudo Cyanine| | 2, 2 | =CH-CH=CH- | Carbo Cyanine| | 4. 4 | =CH-CH=CH- | Krypto Cyanine| - They sensitize photographic plates to different wavelengths. Cyanine dyes with heterocyclic bases are used as effective sensitizers. Image showing the general structural formula of other types of cyanine dies. - For example, Benzthiazole and Benzimidazole, are the effective sensitizers of green color. - Image showing two different examples of cyanine dyes that are good sensitizers. * **Merocyanine dyes**: - They have one ‘N’ and ‘O’ at auxochrome. They are a valuable class of photographic sensitizers. Image showing the general structural formula of Merocyanine dyes. - Examples: Image showing different types of merocyanine dyes. * **Oxonole dyes**: - *They contain two ‘O’ atoms as auxochrome*. They are poor sensitizing dyes. - They can be used for application like color filters: - For example, Image showing the molecular formula of Oxonole dyes. ## Indicator dyes: - The first dye, used *as indicator was litmus*. It is extracted from a *seille lichen*. - It is in, blue or red color. It present day many dyes have found application in *analytical chemistry* as an indicator. 1. **As pH indicator (Acid-Base indicators)**: - For example, phenolphthalein, methyl red, methyl orange, congo red, picric acid, malachite green, crystal violet, etc. - Within certain pH range, there is a structure change in indicator dye & color of the indicator dye changes (photochromism). 2. **Redox (Oxi-Red) indicators**: - For example, methylene blue, indigo carmine, indigo. Image showing chemical reaction showing Indigo with concentrated H2SO4 or Oleum 3. **As Adsorption indicators**: - In volumetric analysis in the titration of halides (Br, Cl, I) with AgNO3, for example: di-chloro fluorescein, eosin, etc. 4. **As precipitants for determination of metals**: - For example: safranine, methylene blue. 5. **Metal complexometric/pH indicators**. ## Indigo dye: - It is known in India for many centuries. - The ancient Romans & Egyptians had knowledge of indigo. - Indigo has been isolated from several plants. From genus "Indigo fara" grown in India and China. - Colouring matter as such, do not occur in the indigo plant, Image showing the chemical conversion of Indican to Indoxyl. - Native indigo contains besides indigotin: 1. Indisubin 2. Indigo brown 3. Gluten 4. Indigo yellow 5. Mineral water - Due to this dying properties of natural and synthetic indigo are not identical. Natural indigo is having better properties. - Indigoid dyes are not colours applicable to both cellulose (cotton) and proteins fibres (wool and silk). - Its fastness properties are better for protein fibres. The constitution of indigo was determined by beayer. It is one of the classes of organic chemistry. - The thiol indigoid dyes, have better properties than indigo dyes. - Thioindigoids are used in wool dying and calico printing. - *Indigo absorption* is in red-blue region. -*Thio indigo absorption* is in red region. ## Nomenclature and Classification : - They contain chromophoric group, *one dione (-C-C=C-C-)*.

Dyeing Process and Properties PDF

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