Dyes

Reactive dye is a class of highly coloured organic substances, primarily utilised for tinting textiles, that attach themselves to their substrates by a chemical reaction that forms a covalent bond between the molecule of dye and that of the fibre. The dyestuff thus becomes a part of the fibre and is much less likely to be removed by washing than are dyestuffs that adhere by adsorption.

The very first fibre-reactive dyes were designed for cellulose fibres, and are still used mostly in this way. There are also commercially available fibre-reactive dyes for protein and polyamide fibres. In theory, fibre-reactive dyes have been developed for other fibres, but these are not yet practical commercially. The dyes contain a reactive group that, when applied to a fibre in a weakly alkaline dyebath, form a chemical bond with the fibre. Reactive dyes can also be used to dye wool and nylon, in the latter case they are applied under weakly acidic conditions.

the most important characteristic of reactive dyes is the formation of covalent bonds with the substrate to be colored, I. E. The dye forms a chemical bond with cellulose, which is the main component of cotton fibers.

fiber reactive dye is the most permanent of all dye types. Unlike other dyes, it actually forms a covalent bond with the cellulose or protein molecule. Once the bond is formed, what you have is one molecule, as the dye molecule has become an actual part of the cellulose fiber molecule. No wonder you can safely wash a garment that has been dyed in bright fiber reactive colors with white clothing, a hundred times, without endangering the whites in the least - even if it is all different bright colors, or even solid black! In contrast to all other dyes the reactive dyes bind chemically to the textile fibres, significantly improving the product's colour stability and washability. Thus reactive dying of cotton is currently the most widespread textile dying process in the world.
 
we 'megha international' engaged in manufacturing of dyestuffs since last one decade. Reactives dyestuffs are one of series apart from the direct acid & acralic range of dyestuffs.

'megha international' presents the textile dyers & printers with a very wide range of reactive dyes, which are suitable to various dyeing & printing of cellulose fibre.

dycrofix 'm' dyes : these are called 'cold brand dyes' these dyes are having very good reactivity fastness properties. These dyes require milder alkaline contitions for applications & fixation at the optimum temperature of 25-35 deg. C.

dycrofix 'h' dyes : these are named as 'hot nramd dyes' these dyes are applied under strong alkaline conditions at high temperature of application compared to 'm' dyes. These dyes contains very good fastness properties to wash, perspiration, light etc. These dyes are suitable particularly for printing cotton, viscose, cuprammonium raysons & natural silk.

dycrofix vynil sulphone dyes : these are vinyl sulphone based reactive dyes widely used for dyeing & printing of cellulosic fibres for its very good fastness properties. These dyes are having very good features like, good solubility even in presence of alkali, very good fastness properties, can be applied both by exhaust & padding methods, possesses less affinity hence very good leveling property & suitable for resist & discharge printing very much effectively. These dyes are applied by exhaust method at the optimum temperature of 60-65 deg. C.

dycrofix 'he' : these are bifunctional reactive dyes. Which are having two reactive molties of the same type viz monochloro triazinyl. The chromogen of the colour is supported through a stillbene in the molecule. This structure provides good light fastness and as well good washing fastness because of having high molecular weight.

Dyeing is normally done in a neutral or slightly alkaline dyebath, at or near the boil, with the addition of either sodium chloride (nacl) or sodium sulphate (na2so4). Also known as hot-water dye, this type can be used with hot tap water and requires no leveling or exhausting agents. It is convenient but lacking in light-fastness and wash-fastness. Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as ph indicators and as biological stains.

Direct dyes are another class of dyes, one of the two types of dyes that are mixed in 'all purpose' dyes such as rit. (the other type in the mixture is an acid dye, which will not stay in any cellulose fiber for long. ) the colors of direct dyes are duller than those provided by fiber reactive dyes, and the wash fastness is poor - except anything dyed with them to 'bleed' forever. The one advantage is that direct dyes may be more lightfast, that is, resistant to fading in the light, than fiber reactive dyes. The "direct dye" classification in the color index system refers to various planar, highly conjugated molecular structures that also contain one or more anionic sulfonate group. It is because of these sulfonate groups that the molecules are soluble in water. Though most direct dyes still can be obtained in powder form, it is increasingly popular to receive them as liquid concentrates. The advantage of concentrates is that they are easy to handle and meter. The disadvantage is that the surfactants and co-solvents needed to keep the dye concentrates stable may interfere with retention and sizing in the case of very deeply colored grades.

 

Acid dyes are water soluble anionic dyes which are applied to fibres such as silk, wool, nylon & modified acrylic fibres from neutral to acid dyebaths. Attachment to the fibre is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fibre. Acid dyes are not substantive to cellulosic fibres. Acid dyes are used both commercially and by the studio dyer to dye protein/animal fibers such as wool, silk, mohair, angora, alpaca and some nylons and synthetics. Acid dyes require the use of an acid such as vinegar, acetic or sulphuric acid to set the color. acid dyes sound scary to some novices, who imaging that the dyes themselves are caustic strong acids. In fact, the dyes are non-caustic, are in many cases non-toxic, and are named for the mild acid (such as vinegar) used in the dyeing process, and for the types of bonds they form to the fiber. Some of them are significantly more toxic than fiber reactive dyes, while others are even safe enough to eat, and are sold as food coloring.

acid dyes are classified into several classes: 1, leveling acid or strong acid dye, 2, super milling or fast acid or neutral acid dyes 3, milling or weak acid dyes, and. Leveling acid dyes are been sold under the trade names of kiton, erio, intracid, sandolan, and amacid, among others; they are also the acid dye component of all-purpose or union dyes such as rit and tintex, says knutson. It's difficult now to find out which specific acid dyes fall into which of these dye classes, however. At least part of the reason is that the information is not particularly useful to the dyer.

 

most histologic dyes are distinguished as acid or as basic dyes. An acid dye exists as an anion (negatively charged) in solution, while a basic dye exists as a cation (positive charge). For instance, in the hematoxylin-eosin stain (h&e), the hematoxylin-metal complex acts as a basic dye. The eosin acts as an acid dye. A very large class of dyes containing acidic groups, such as the sodium salts of sulfonic acids or phenolic groups. They are more soluble and have less tinctorial value than basic dyes but they also have greater light fastness. They do not form lakes with tannin. Acid dyes are used in dyeing leather, paper, etc. , and their particular value lies in their ability to produce brighter, more uniform colors. They are normally applied from an acid dye liquor (acetic, formic, or sulfuric acid); however, unless applied from a neutral or only slightly acid dyebath, I. E. , ph of 6. 0 to 7. 0, their use is likely to result in acid degradation of the material dyed.

Basic dye is a stain that is cationic ( ve charged) and so will react with material that is (ve) negatively charged. The cytoplasm of all bacterial cells have a slight negative charge when grown in a medium of near neutral ph and will therefore attract and bind with basic dyes. Some examples of basic dyes are crystal violet, safranin, basic fuchsin and methylene blue. It’s applied to wool, silk, cotton and modified acrylic fibres. Usually acetic acid is added to the dyebath to help the take up of the dye onto the fibre. Basic dyes are also used in the coloration of paper.

Basic dye is a class of dyes, usually synthetic, that act as bases, and which are actually aniline dyes. Their color base is not water soluble but can be made so by converting the base into a salt. The basic dyes, while possessing great tinctorial strength and brightness, are not generally light-fast; therefore their use in the dyeing of archival materials is largely restricted to those materials not requiring this characteristic. Basic dyes were at one time used extensively in dyeing leather, mainly because they are capable of combining directly with vegetable-tanned leather without the use of a mordant. Basic dyes show virtually no migration in acrylic fibers under normal dyeing conditions, compatibility is of major importance in selecting dye combinations with optimum level dyeing behavior.

Basic dyes possess cationic functional groups such as -nr3+ or =nr2+. The name 'basic dye' refers to when these dyes were still used to dye wool in an alkaline bath. Protein in basic conditions develops a negative charge as the -cooh groups are deprotonated to give -coo-. In an electric field the chromophore ion travels to the cathode or negative pole; it is positively charged. Generally forms salts with negatively charged (acidic) substances in tissue (chromatin, ergastoplasm, cartilage matrix, some granules). Affinity for such dyes, is called basophilia. Basic dyes perform poorly on natural fibres, but work very well on acrylics.


The most common anionic group attached to acrylic polymers is the sulphonate group, -so3-, closely followed by the carboxylate group, -co2-. These are either introduced as a result of co-polymerisation, or as the residues of anionic polymerisation inhibitors. It is this anionic property which makes acrylics suitable for dyeing with cationic dyes, since there will be a strong ionic interaction between dye and polymer (in effect, the opposite of the acid dye-protein fibre interaction).

Solvent dye is a dye which is soluble in an organic solvent and is mostly introduced in the form of a solution in an organic solvent.

dyes are generally defined along the lines of being coloured, aromatic compounds that can ionise. One class of dyes is an exception to this. These colour by dissolving in the target material, which is invariably a lipid or non-polar solvent. The colour index uses this as a classification and naming system. Each dye is named according to the pattern: solvent  base colour number. these dyes are thereby specifically identified as dyes of the stated colour, and whose primary mechanism of staining is by dissolving. Note that this is a functional and colour classification. It contains no chemical information, neither does it imply that dyes with similar names but unique numbers are in any way related. It should also be noted that the classification refers to the primary mechanism of staining. Other mechanisms may also be possible, but are rare.

as a general principle, solvent dyes do not ionise. Many are azo dyes which have undergone some molecular rearrangement and lost the ability to ionise. In the process they gained the ability to dissolve in non-polar materials such as triglycerides. They are commonly used to stain such materials in sections. They are frequently called lysochrome dyes. Lyso- meaning dissolve, and -chrome meaning colour.

Mordant dyes are those dyes which require a mordant in their application and which upon combination with the mordant deposit insoluble color on the substrate, E. G. , dyes with metal chelating groups. Like the name suggests these dyes require a mordant. Mordants are substances of organic or inorganic origin which combine with the coloring matter and are used to fix the same in the production of the color. For the purpose of this class, such materials as oils and sulfonated oils, soaps, fats and higher acids, are not generally considered as mordants, but as coming within the scope of “assistants” in dyeing.

the mordant substances include such acids as tannic acid, sumac, gall nuts, bark extracts, oleic and stearic acids, and turkey red oil; and metallic substances such as various combinations or soluble salts of chromium, aluminum, iron, copper, and tin. The latter, the metallic mordants, are more used than the acid mordants. Mordant improves the fastness of the dye on the fibre such as water, light and perspiration fastness. The choice of mordant is very important as different mordants can change the final colour significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques.

dyes are generally defined along the lines of being coloured, aromatic compounds that can ionise. Although this definition infers that ionic interaction with oppositely charged tissue constituents is the norm, there are exceptions. Some dyes require the presence of a metal to properly develop their colour or staining selectivity. These are termed mordant dyes. The colour index uses this as a classification and naming system. Each dye is named according to the pattern: mordant + base colour + number.

 

these dyes are thereby specifically identified as dyes of the stated colour, and whose primary staining mechanism requires the presence of metal atoms. Note that this is a functional and colour classification. It contains no chemical information neither does it imply that dyes with similar names but unique numbers are in any way related. It should also be noted that the classification refers to the primary mechanism of staining. Other mechanisms may also be possible.

 

the most commonly used mordant dyes have hydroxyl and carboxyl groups and are negatively charged, i. E. Anionic. It is convenient to view these as a specialised subgroup of acid dyes. Some other mordant dyes may possess amino groups, and are cationic overall. Despite this, they must still have hydroxyl or carboxyl groups, since lake formation requires it. Mordant dyes can usually stain by ionic interaction in the same way as other ionisable dyes. The colour is often pale, sometimes so pale that the results have no value.

it is often noted that when a mordant dye forms a lake with a metal, there is a strong colour change. This is because metals have low energy atoms. The incorporation of these low energy atoms into the delocalised electron system of the dye causes a bathochromic shift in the absorption. It is this delocalised electron system which is fundamentally responsible for colour in dyes. Since different metal atoms have differing energy levels, the colour of the lakes may also differ.

the most commonly used mordant dye is undoubtedly hematein (natural black 1), whose status as a natural product supercedes its mode of dyeing, apparently. Others are eriochrome cyanine r (mordant blue 3) and celestine blue b (mordant blue 14), both used as substitutes for alum hematoxylin but with a ferric salt as the mordant. Alizarin red s (mordant red 3) is valuable for the demonstration of calcium, particularly in embryo skeletons.

Vat dyes are those dyes which are applied to the substrate in reduced, soluble form and then oxidize to the original insoluble pigment. Common vat dyes are quinonic dyes and particularly common are anthraquinones and indigoids. These dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye. In this leuco form these dyes have an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. Most vat dyes are less suitable than, say, fiber reactive dyes, for the home dyers, as they are difficult to work with; they require a reducing agent to solubilize them. Indigo is an example of this dye class.

vat dye is obtained through oxidation. It is usually very bright and will hold up better when bleached than most other dyes. The process is very colorfast in all respects. This is an expensive procedure and is used mainly on high-end products. Vat dyes include the natural dyestuff, indigo, and the artificial dyes called by the trade names, indanthrene, and flavanthrene. They are called vat dyes because, being originally insoluble in water, they undergo special preparation in large vats before the cloth is introduced; here they are made soluble, usually by the adding of caustic soda and hyposulphite. In this mixture or dye liquor the textiles are soaked. Certain chemicals are thereafter added, changing the dyestuff back to the insoluble form in the cloth or fiber. This is called the fixing process. All the vat dyes are fast, especially to washing. The artificial vat dyes have in many instances taken the places of the older mordant dyes, and their future seems promising, for they are cheaper and easier to apply than the mordants, although not so cheap and convenient as the direct dyes.

both cotton and wool, as well as other fibers, can be dyed with vat dyes. "vat dyeing" means dyeing in a bucket or vat. It can be done whenever a solid even shade, the same color over the entire garment, is wanted, using almost any dye, including fiber reactive dye, direct dye, acid dye, etc. The opposite of vat dyeing is direct dye application, such as, for example, tie dyeing. "vat dyes" are a special class of dyes that work with a special chemistry.

 

We offer Metal Complex Dyes to cater the demand of various industries like paint and textile . Metal Complex Dyes are known for its fastness properties and hence find application in dyeing of wool, nylon, silk. Further our range of Metal Complex Dyes manufactured as per the prevailing quality standards.

Brief Process Of Rapid Fast (Azoic) Dyes On Cotton/ Viscose Textiles.

The Rapid Fast are stabilized Azoic Dyestuffs specially prepared for printing. They are applied to the fiber in one operations. When developed under acid condition bright full shades are obtained which possess very good fastness properties. Due to cross coupling which may occur between certain Rapid Fasts, proper care should be taken when using mixtures of Rapid Fast as resultant shade obtained is un-predictable. Dyestuffs of others groups may be used to supplement the color range, particularly for greens and blues. As the Rapid Fast can be developed by either neutral or Acid ageing colors of Rapid Fast vat or Rapid Sols may be printed alongside. In some cases Rapid Sols can also be printed in admixture with Rapid Fast eg., For producing Green shade, Rapid Fasts are largely used in block and screen printing, some printers prefer particularly for Rapid Fast L.Y. 3 GH, RED RH, G.Y. 2 RA, G.Y. IGK, to expose undeveloped print to sunlight and then acid developed.

Rapid Fast Dyestuffs (Powder)	50 Parts	40 parts
Caustic Soda Solution (1:2) 33% W/W	30 Parts	30 Parts
Methylated Spirit	20 Parts	20 Parts
Boiling Water	200 Parts	200 Parts
Thickening (Neutral)	695 Parts	700 Parts
Wetting Agent	5 Parts	5 Parts
	1000 Parts	1000 Parts

We offer our clients a wide range of Ink dyes which is widely used for making inks and coating. Our dyes are extensively used in diverse industries and finds diverse application. These dyes are formulated using quality material and undergo stringent quality tests to offer optimal satisfaction to our clients.