Dyeing | Coirboard

Coir Processing – Technology and Machinery

Dyeing

Dyeing of coir fibre/yarn is essential for improving the marketability and aesthetic value of coir products and according to customer taste. A dyestuff is most commonly an organic compound, which can be used to impart colour to a substance. A Wide range of dyes capable of yielding bright shades of excellent fastness are available for the dyeing of yarn.
In dyeing, the fibre absorbs the dye from the aqueous solution is more or less uniformly coloured. The uniformity of dyeing depends upon the absorptive power of coir fibre, the nature of the dye and condition of dyeing. The dyed shade usually must be matched against a sample and the fastness of the dyeing must conform to the specified requirement of the consumer.

Traditional method of dyeing coir

In the conventional method, the dyeing is carried out in copper or aluminium/Indalium or G.I. vat of 1.2 M diameter and 0.75 height place on hearth made out of country bricks, fired from below using country wood. The dye vat is sufficient to process 60 kg. of coir yarn or 30 kg. coir fibre with a material to liquor ratio of 1:12 for coir yarn and 1:20 for coir fibre.
After filling with required quantity of water, it is heated from below till the required temperature is reached. The required quantity of dyestuffs and chemicals are added to the dyebath after making into a paste. The dyebath is stirred well and the material is entered and turned manually at frequent intervals for level dyeing. At the end of dyeing the material is taken out washed in cold water and dried under shade.

Improved method of dyeing coir

The improved method of dyeing process is carried out by highly skilled professionals in the industry using dye vats made of stainless steel and fitted with drainage valve for proper draining of dye effluents.
The vats are fixed on hearths made of firebricks with flue pipes for efficient air draught for maximum utilisation of the heat energy. The dyes are taken as per recipes formulated by the Central Coir Research Institute (CCRI), which is available in the shade cards. The quality of dyeing is improved compared to the traditional method of dyeing.

Mechanised System of Dyeing

In the mechanised system of dyeing, coir yarn is dyed, comprising of dye vats with forced circulation of the dye liquor in two-directions on uniformly arranged coir yarn for uniform level dyeing. The temperature is controlled as per the requirement by regulating the flow of heating system. After the dyeing operation, hydro-extractors are used to drive out of the major part of the mechanically held up water and finally these materials are dried on the endless conveyor dried, for efficient drying. This system of dyeing helps to improve the penetration, shade consistency, uniform dyeing on coir fibre/yarn by the action of temperature efficient and forced circulation of dye liquor and period of dyeing. This method help to dye large quantities of material at a time avoiding shade variation compared to the other two processes.

The classes of dyes used in coir industry

Dyes belongs to the classes of Basic Acid and Direct dyes are suitable for achieving better fastness properties, penetration and brilliant shade with less cost are common in use in coir industry. These dyes are applied to the materials from their solutions in water with the aid of chemicals like acetic acid, sulphuric acid, formic acid, common salt etc. This facilitate the transfer of dyes from the dye bath to the fibre/yarn under appropriate conditions of temperature for specified periods depending on the dyestuff that is being used. The basic dyes have high tincture value and affinity to coir but are fugitive to light and rubbing. The acid dyes have better fastness to light but of less brightness than basic dyes. Direct dyes find use in producing shades having fastness properties better than acid dyes but they produce dull shades and require longer processing time.

Dyeing of coir with reactive dyes (ATIC – Procion Brand cold dyeing)

The dye bath is set with the required quantity of dyes stuffs dissolved in water in cold ( 1:10 m:l ratio) with half the required quantity of salt. The wetted/coir yarn is entered and treated for 20 minutes. The remaining part of the salt is added and worked for another 20 minutes. Half of the prescribed quantity of soda ash is then added and worked for 15 minutes. After wash the remaining part of soda ash is also added and worked for 20 minutes. 10 gl litre urea is added in the dye bath for fixing the dyes to the material at the final stage of dyeing and the material is allowed to remain in the bath for 15 minutes. After dyeing, the material is taken out, squeezed and washed in cold water. Finally the material is soaped with 3 grams per litre soap at boil for nearly 15 minutes, to remove the excess dye stuffs. The material is thoroughly washed in cold water and dried in air under shade. During the process of drying the material is subjected to thorough agitation to have excellent contact of the material with the dye liquor.
The major quantity of dyeing of coir fibre/yarn is done in the small-scale sector using conventional process. With a view to improve the quality of dyed material, modern dyeing methods are also adopted by the industry.

Coir dyeing with Nucifex dyes from Triade BV Rotterdam

The Nucifix dyestuffs range is specially developed for natural fibre such as coir yarn etc.

Compatibility

Nucifex dyes ranging with their almost similar dyeing properties, they can be freely applied together in combination.

Substrate		Bleached coir yarn
Types of Dyes		Nucifix
% based on		Yarn dry weight
Process Dyeing
Fresh bath	1:15	Liquor at 50 C
	X %	Nucifix dyes Run 10 min at 50 C, followed raise temperature to 80-85 C. Continue dyeing for 90 min.
Add	1-2%	Formic acid (1:10) Run 30-45 min.
Aftertreatment (Use fresh bath)	0.5-2 %	Fixing agent (improves wet fastnesses)
Cool down, rinse very well and drying

Bleaching

Bleaching of coir fibre/yarn is essential for improving the colour. This is widely used in coir industry for the purpose of ornamentation of coir products. There are certain shades of dyestuffs to be used in the production of coir matting/carpets, which require bleaching of yarn to improve its penetration and brightness especially in the case of pastel shades.
It is estimated that about 20% of the coir yarn/fibre used for the manufacture of coir mats, mattings rugs and carpets are made out of bleached coir yarn in the coir industry. Bleaching of coir fibre/yarn is generally being carried out using hydrogen peroxide.
The oxidation process using hydrogen peroxide is in vogue in the coir industry. There are two process followed in the industry viz; Hot and cold process. It is also observed that none of the factories are using imported chemicals for bleaching of coir materials. Generally, the chemicals used for bleaching are hydrogen peroxide and sodium silicate. However, there are wide variations in the recipe of different factories as well as the degree of whiteness.
For Standards and specification of dyes and dyeing click here