The chemistry of the leuco form of vat dyes is rather simple. Indigo water insoluble leuco form water soluble textile coloration is by far the most important application of vat dyes but a wide variety of other applications have also emerged, often requiring dyes with specific chemical structures. Vat dyes are a unique class of dye, similar to indigo. This leuco form of the dye allows the transfer of the dye from the surface of the fiber to the interior region of the cotton fiber. Leuco vat dyes are employed to produce brighter shades from oxidative dyes in oxidative haircoloring systems and processes. Solubilised vat dyes are less rapidly taken up than are the more conventional vat dyes and are mainly used for the. Leuco dyes colorless leuco dyes and thermochromic leuco dyes. Some leuco quinones are quite stable in the solid state and can be stored for a year. The process of converting insoluble vat dyes into soluble form is known as vatting. Vat dyes generally offer superior fastness properties. Automated extraction of direct, reactive, and vat dyes from. Vat dyes are a class of dyes that are classified as such because of the method by which they are applied. Ch emi stry o f i n d i g o artsnow learning teaching and.
Oxidative hair dye compositions and processes utilizing leuco vat dyes. A leuco dye is a dye whose molecules can acquire two forms, one of which is colorless. The purpose of the reduction step is to change the dyestuff from a waterinsoluble form, using a suitable reducing agent with an alkali, to a watersoluble form. Indigo is a socalled vat dye, which means that it needs to be reduced to its water soluble leucoform before dyeing.
Dyeing process of vat dye leuco knowledge sinoever. The chemistry and manufacture of vat dyes by robert j. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed. This form is soluble and has substantivity for cotton. Leuco dyes form the basis of thermal printer papers and certain ph indicators. In what type of garments vat dyes are normally used. The prepigmentation dyeing methods are simple processes in which a fine dispersion of the vat pigment is uniformly circulated through the goods that are then treated with alkaline hydros solution to cause reduction.
Vat dyes, which include indigo and anthraquinonebased dyes, are chemically complex dyes which are insoluble in water. Color fastness to crocking improvement of indigo and. The shutdown of the connect chemicals factory and the subsequent shortage of leuco dye put a tight squeeze on the worlds thermal paper supply chain and resulted in late and missed orders, increased costs and even caused bankruptcies of companies who rely on the dye for production. The products found in forms of slurry, powder, solventbased ink, epoxy, master batch, etc. Based on temperature, amount of caustic soda, hydrosulphite and salt, used in dyeing, vat dyes can be classified into four main groups. Solubilization of hydrophobic dyes in surfactant solutions. The soluble leuco dye permeates the cellulose structure during the dyeing process and then is oxidized. Functional groups in the insoluble pigmentary form, all vat dyes have a common chemical feature. About 50 ml dimethylsulphoxide dmso solution of the 1. Chemistry and applications of leuco dyes edited by ramaiah muthyala from chemical topology to threedimensional.
Vat dyes typically do not possess ionic groups and are insoluble in water. Vat dyes are used in the dyeing and printing of all types of cellulose fibres, and also of blends of cotton with polyester. March 15, 2009 i introduction vat dyes, which include indigo and anthraquinonebased dyes, are chemically complex dyes which are insoluble in water. Expired lifetime application number us585941a inventor justin a mcsheehy. Vat dyeing process textile dyeing process with vat dye vat dyes. Indigo is a socalled vat dye, which means that it needs to be reduced to its water soluble leuco form before dyeing. The application method for sulphur dyes is analogous to that for vat dyes.
Sep 27, 1994 because the industry has not found an acceptable process for forming the leuco form of vat dyes the industry has turned to the formation of indigosols, the sulfuric esters of the leuco form of vat dyes. A process for reducing vat dyes, such as indigo, into their leuco form by placing a metal, such as aluminum, in water in the presence of a reduction facilitator to form a first solution after which a vat dye having the general structure o cc c n c o where n1, 2 or 4 is mixed with the first solution to form a dye solution where substantially all of the vat dye is reduced to its soluble. Vat and sulphur are the two types of dyes involving a reductionoxidation mechanism. The dyeing of supermicrofibre nylon with acid and vat dyes. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat. Vat dyes are widely used for colouring cellulosic fibre, especially cotton fibre along with viscose rayon, leather and other fibres. This method of reduction and application is the source of the name for this class of dyes. Vat dyes have lots of properties which are required to remember before and during dyeing process. Us5364415a oxidative hair dye compositions and processes. Structures iiii have been proposed for ci leuco sulphur black 1 5. This is characteristically purple but is also completely insoluble in water, meaning that it. Indigo dye is the most used vat dye as it becomes the base for dyeing denim fabrics.
The purpose of the reduction step is to change the dyestuff from a waterinsoluble form, using a suitable reducing. The reduced form is called the leuco vat acid, and is applied from an alkaline. The vat dyes are naturally coloring matter and kept in wooden vat and make solubilise vat dyes by reduction so it is called vat dyes. Heres why a leuco dye shortage has plagued thermal paper. The alkali soluble leucovat dyes were, of course, extremely important in textile dyeing, as they provided the only means by which the highly insoluble parent vat dyes could be applied permanently to the fabric. While continuous dyeing with vat offers economic advantages, several precautions are required to ensure a satisfactory result. Dyeing of cotton with vat dye part 01 textile study center. What is vat dyes properties of vat dyes textile fashion. Vat dyeing process textile dyeing process with vat dye. Unlimited viewing of the articlechapter pdf and any associated supplements and figures. It reduces insoluble vat dye to partially soluble leuco dye, counteracts effect of dissolved oxygen in.
To be applied to cotton, vat dyes must first be reduced from the keto form to the watersoluble leuco form using a reducing agent such as sodium dithionite. The term leuco, meaning white and was applied to the reduced form of vat dyes. Since vat dyes are manufactured as the insoluble pigment known also as the oxidized form of the dye, they must be chemically reduced to the soluble or leuco. Vat dyes vat dyes are insoluble in water and cannot be used directly for dyeing.
A solution of the leuco form can be applied for dyeing or printing. Water carries the soluble form, leucoindigo, as it soaks through the material in the vat. The regenerated leuco compound may then be oxidized back to the pigment form. They require a reducing agent, thiox, an alkali and lye not available on our website. An approach to the influence of particle size distribution of. The most common example is in applying sulfur dyes and vat dyes. Sep, 2014 leuco dyes certain leuco dyes insoluble in water. Cotton, wool, leather and other fibers can be all dyed. In dye bath the pigment is converted into a watersoluble form using a strongly. Because vat dyes are sold as pigments, it is important to be. Leuco dyes are normally associated with polymethines, particularly with dior triarylmethines. The reduced form is quite stable in presence of naoh to carry out dyeing at room temperature. The pigment form, however, has no substantivity for cotton at all.
L ong before the advent of systematic physical sciences and the growth of the chemical industry, as long as 5000 years ago in india, dyeing methods were. The alkali soluble leuco vat dyes were, of course, extremely important in textile dyeing, as they provided the only means by which the highly insoluble parent vat dyes could be applied permanently to the fabric. Change color on oxidation or with fluctuating of temperatures. In the 19th century were the synthetic dyes developed and nowadays indigo is mainly synthesized from byproducts of fossil fuels. They require lye, thiox, and a temperature of 120 to 140 f in a dyebath. Leuco vat blue 1 is an organic compound with both amine and alcohol substituents.
The amount of heat that is evolved per mole of amine in a neutralization is largely independent of the strength of the amine as a base. The chemical structure and commercial forms of vat dyes are also covered. Qualitative and quantitative analysis of vat dyes by paper. Synthesis of a new indigo vat dye 71 reduction of the dye. Use of this class name, which is more or less parochial to the technology of dyes, is not endorsed. Therefore, they are reduced to a colourless soluble form leuco in large wooden vats with a reducing agent such as an alkaline solution of sodium hydrogensulphite. Other vat dyes are reduced at a temperature depending on the class of dye table 8.
Indigo water insoluble leuco form water soluble textile coloration is by far the most important application of vat dyes but a wide variety of other applications have also emerged, often requiring dyes. Classification according to affinity for fibre vat dyeing conditions can vary widely in terms of temperature and the amount of salt and alkali required, depending on the nature of the dye applied. Method of reducing vat dyes and the process of dyeing. Nmr spectroscopy is a useful technique for the identification and characterisation of this traditional class of. The original vat dye is indigo, once obtained from plants but now produced synthetically. Aspland, school of textiles, clemson university, clemson, s. Dyeing auxiliaries function of auxiliaries dyeing method. The leuco form is produced by reduction with a sulphur compound traditionally alkaline sodium sulphide. Leuco vat dyeing, prepigmentation, semi pigmentation and batch after treatments are covered in this article. Vat dyes are most important dyes for dyeing and printing on cotton and cellulosic fibres. Thermochromic dyes are based on mixtures of leuco dyes with suitable other chemicals, displaying a color change usually between the colorless leuco form and the colored form in dependence on temperature. Once attached to the fabric, the leuco dye is then oxidized to the insoluble state which is. Color fastness to crocking improvement of indigo and sulphur. The practical details of using vat dyes in both batch and continuous processes are covered in this second and final part of chapter 3.
Method of reducing vat dyes and the process of dyeing fabrics. Nowadays, most of the industrial reduction is performed chemically by sodium dithionite. The present invention relates to novel leuco vat dye preparations in granule form comprising as essential constituents a leuco vat dye, an alkali metal hydroxide and a mixture of from 10 to 100% by weight of an. Dyes used for denim dyeing a description denim jeans. The colorless form is sometimes referred to as the leuco form. An approach to the influence of particle size distribution. Dinitroaniline, chemical evidence, indigo dye, reduction. Vat dyes are insoluble in water but it becomes in soluble form by vatting process. Vat dyes are a unique class of dye, similar to indigo, which go through a process of reduction and then oxidation when applied to plant fibers. Almost any dye, including fiber reactive dyes, direct dyes, and acid dyes, can be used in a vat dye. Vat dyes are the wellknown dyes they are insoluble in water and hence cannot be used directly for dying.
Since vat dyes are manufactured as the insoluble pigment known also as the oxidized form of the dye, they must be chemically reduced to the soluble or leuco form of the dye. This paper concerns the dyeing of artificial nylon suede with both the alkali and acid leuco forms of vat dyes and compares the resulting dyeings with those obtained using 1. But on reduction to a leuco form colour less, they become soluble in an alkali and acquire affinity for cellulose fibres. Dyeing process of vat dye leuco oct 02, 2019 when the vat dye is immersed, the initial dyeing rate is very high, but it is only adsorbed on the surface of the fiber in a ringdyed state, and then slowly diffuses into the interior, showing slow dyeing characteristics and poor transferability. But vat dyes fastness properties is good among the all dyes.
They must first be reduced to the leuco form in an alkaline solution of sodium hydrosulfite before application to the cotton or rayon fiber. Potential drawbacks to selecting vat dyes include a tendency for phototendering and a limited color gamut. When the material is exposed to the air or another source of oxygen such as welloxygenated water the leuco indigo oxidises to blue indigo particles that physically lodge in the material. Dyeing of cotton with vat dyes dye sodium hydroxide. The vat dyes are naturally obtained coloring materials from the ancient time and kept into wooden vat and make soluble in vat by the process of fermentation so it is called vat dyes. Chemistry and applications of leuco dyes request pdf. Reductive discharge inkjet printing of predyed textile.
Pdf on feb 12, 2012, rahul oza and others published general. Your can restrict your selection by using the other filters. By operating in a nitrogen atmosphere, it has been found possible to effect chromatographic separations of vat dyes in leuco form on strips of paper or synthetic fibres. They must first be reduced to the leuco form in an. Once it has been converted to its soluble leuco form, the vat dye can. Inkodye is a type of vat dye that uses light rather than oxygen to fix the dye, with a. Water carries the soluble form, leuco indigo, as it soaks through the material in the vat. Photophysical and spectroscopic studies of indigo derivatives. Vat dyes cant be directly applied and required vatting because it is insoluble in water. Vat dyes are a class of dyes that are classified as such because of the method by which they. The indigo derivatives are generally known as vat dyes and are insoluble in water in their oxidized colored form, the keto species. Once the vat dyes have been regenerated inside the fiber, they are very insoluble. Based on the substantivities of leucovat anions, the. Nmr spectroscopy is a useful technique for the identification and characterisation of this traditional class of vat dyes.
Before chemical reducing agents were readily available, vat dyes were converted to their soluble leuco form by fermentation of organic matter in wood tubs called vats. Chemistry and application of leuco dyes slideshare. In their coloured form they are insoluble pigments, so their applications depend on reversible reductionoxidation redox reaction. Vat dyes are one of the important class in the synthetic dyes produced. Reductive discharge inkjet printing of predyed textile fibres. Us2898337a us585941a us58594156a us2898337a us 2898337 a us2898337 a us 2898337a us 585941 a us585941 a us 585941a us 58594156 a us58594156 a us 58594156a us 2898337 a us2898337 a us 2898337a authority us united states prior art keywords leuco ph process vat dye oxidation prior art date 19560521 legal status the legal status is an assumption and is not a legal. Dec 28, 1999 leuco vat dye preparations in granule form. Leuco dyes are a key component of some thermochromic dyes and thermal printer papers, photochromic materials, and of the flexplay dvd discs with limited play time, where leuco form of methylene blue is used. The reduction and esterification of the vat dye produces the sulfuric ester instead of the leuco form of the vat dye. When the material is exposed to the air or another source of oxygen such as welloxygenated water the leucoindigo oxidises to. The analysis of indigoid dyes as leuco forms by nmr. Based on the substantivities of leuco vat anions, the traditional classification system for vat dyes offers batch dyers a better means for selecting vat dyes to be used successfully in combination. Under these conditions, the leuco form develops affinity for.