Improving levelness in vat dyeing
The following techniques are useful for dyes that don't have adequate levelling capabilities to achieve an even shade and good fastness properties.
(ii) Use of levelling agents.
(iii) Use of pigmentation methods.
Method of Vat Dyeing
Vat dye may be applied to Cellulose textiles by any of the following procedures -
Explanation -
(A) Leuco vat dyeing :
With the help of hydrated oxide and sodium hydrosulphite, the insoluble dyestuff is transformed into its soluble and substantive form (leuco-vat form) before application during this procedure.
Either bulk vatting or small-scale vatting is used for vaporisation (long liquor method). during this leuco vat form, the dye is absorbed by the fibre and is later converted by oxidation (either chemical or air) and soaping to its original insoluble form.
Aside from the speed of vatting, the dye bath's soluble form implies that the dye's particle size is irrelevant (finer brands are vatted quickly).
Controlling the initial rate of dyeing is additionally crucial, and any of the ways listed below can help with that:
(b) Frequently reversing the flow of liquor through the packages is employed to regulate the speed of dyeing while dyeing yarn (in cheese or beam form) in circulating machines.
(c) Employing extra aids, like retarding agents.
(d) Decreased dyeing rate could be a result of lower dyeing temperature.
(e) Padding technique: Padding is another method that will be accustomed to colour material using the leuco-vat process.
At rock bottom temperature that the soundness of the vatted dye allows, piece items are padded with an answer of the vatted dye.
The utilization of chemicals that penetrate and defoam is additionally beneficial.
The air oxidation, rinsing, and soaping procedures are meted out after padding.
For bulk manufacture of uniform hues, this method works well.
For obtaining satisfactory results. an acceptable padding mangle should be used so that all air is squeezed out before entry of the products within the dye liquor and every one the liquor is withdrawn when the products are leaving the mangle.
Maintaining constant temperature throughout padding entails the best process control. The padding process is especially useful when dyes contain a low affinity for the fibres.
(B) Pigmentation process
In this procedure, dyes are used for dyeing in their original, insubstantial, and insoluble forms, where they compare very favourably to pigments, giving pigmentation its name.
In reality, the event of vat dyes within the type of extremely finely divided particles made it feasible to attain homogeneous dyestuff deposition on yarn and cloth.
In package dyeing, the small dye particles eliminate all likelihood of filtration through yarn.
A required quantity of micro-fine (mt), supra-disperse (sd), and ultra-disperse (ud) dye powder is sprinkled in 10–20 times the maximum amount of warm water (40°C) as its weight to arrange the dyestuff's dispersion.
Pasting should never be through with quandary, a surface-active agent, etc., or in other such situations.
Eventually, lumps form as a result of aggregation.
Fine dispersions and homogeneous deposition are guaranteed by the dye particles' fineness.
The dye is treated with an alkaline reduction liquid at the correct temperature to alter it from its pigment form, which is uniformly distributed throughout the fabric, to its substantive leuco-vat form, which is absorbed by the fibre.
Following the dyeing, step is the customary process of oxidation and soaping. This procedure employs the pad-jig method of dyeing with vat dyes.
(C) Vat-acid process:
In this procedure, non-substantive particles are uniformly deposited and stuck by working in an exceedingly hydrated oxide and hydros solution.
Contrary to pigmentation, which is restricted to the microfine (mf) or super-disperse (sd) brands, the vat-acid technique allows the appliance of any form of vat colour.
The basic idea behind the vat-acid method is made public here.
Leuco-vat acid, an awfully fine dispersion, is made when a vat colour is decreased and treated with carboxylic acid while being mixed with an acid stable dispersing agent.
The subsequent action is often accustomed to illustrating how vat acid is made.
It's crucial to recollect that when there's not enough acid, vat acid isn't generated and precipitation may happen if there's not enough suitable dispersion.
The subsequent are the most traits of the vat-acid process:
(i) Insoluble vat acid is extremely immune to atmospheric oxidation in acidic media. All traces of alkali should be off from the things before applying vat acid.
(ii) it's no affinity for cellulose substrates, but when hydroxide is added, it's easily transformed into a substantial form.
(iii) Alkali neutralisation with ethanoic acid leads to substantially finer dispersions than colouring with micro-fine or supra-disperse brands of vat dyes.
(iv) Vat acid develops relatively more quickly, which lessens dyestuff bleeding within the developing bath.
(v) the strategy is especially interesting for dyeing bulky items, twisted yarns, and finely woven clothing.
Questions -
- What are the methods of vat dyes?
- Describe Leuco-vat dyeing (by Exhaust dyeing or Padding) methods.
- Describe the Pigmentation process for vat dyeing.
- Explain the Vat-acid process for application of vat dye.
References
Hussain, T. (2007, November 19). Important considerations in dyeing with vat dyes. Fibre2fashion.com; Fibre2Fashion. https://www.fibre2fashion.com/industry-article/2701/important-considerations-in-dyeing-with-vat-dyes
Kim, M. R., Kim, H., & Lee, J. J. (2013). Dyeing and fastness properties of vat dyes on meta-aramid woven fabric. Fibers and Polymers, 14(12), 2038–2044. https://doi.org/10.1007/s12221-013-2038-7
Patwary, E. M. Z. (2012, May 4). What is vat dye. Textile Fashion Study; Engr. Mohammad Zillane Patwary. https://textilefashionstudy.com/properties-of-vat-dye-uses/
Saha, S. (2018, October 21). Vat Dyes. Blogger. https://www.onlineclothingstudy.com/2018/10/vat-dyes-indigo-dyes-application-of-vat.html
Sharmin, F. (2017, November 18). Dyeing of cotton with vat dye. Textile Study Center. https://textilestudycenter.com/vat-dye/
The Editors of Encyclopedia Britannica. (2015). vat dye. In Encyclopedia Britannica.
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Writer - Rushikesh Patil (Textile Engineer)
