Fundamentals of Dyeing Basic Terminologies used in Textile Processing

1. DYE AFFINITY

It can be defined as the attraction of the dye to the fibre or the tendency of the dye to go on the fibre on its own without any external influence of heat or chemicals.

2. EXHAUSTING AGENTS

In order to achieve complete exhaustion of the dye bath in a short time, the dyeing rate should be increased. This rate can be increased by adding exhausting agents. These exhausting agents are the chemicals which help in transferring the dye molecules inside the fibre or fabric structure and are important from the point of view of uniform, time saving and economical dyeing, e.g., Common salt which is the most popular exhausting agent in the dyeing of cellulosic fibres with direct dyes.

3. % SHADE

Colour Weighing scaleWhen a textile material is dyed, the shade of the dyeing is expressed as a percentage. Thus when 100gm of cotton yarn is dyed in a dyebath containing 1gm of dye, then it is said to be dyed with 1% Shade. It is the amount of dyes in gms taken for dyeing per 100 gm of textile material. Example, when 2 gm of dye is taken for 100 gms of material, it is said to be dyed with 2% Shade and when 4Kgs of dye is taken for dyeing of 100 Kgs of material, it is said to be dyed with 4% Shade. It can be easily calculated as

% Shade = (Wt of dye taken for dyeing / Wt of material) / X 100

                 = (4kgs / 100Kgs) X 100

                 = 4%

From this it does not follow that all the dye present in the dyebath is taken up by the yarn, unless the exhaustion is 100%. The amount of the dye to be taken for dyeing depends only on the percentage shade and the quantity of the material to be dyed (OWM basis) and not on the Material to Liquor Ratio which determines only the concentration of the dye in the dyebath.

4. M.L.R.

MLR is the ratio of the weight of material in grams to be processed to the quantity of liquor in litres to be used, i.e., the ratio of Material to Liquor.

Example: When 100 Kg of material is dyed by using 1000 litres of Liquor (chemicals + water), the MLR is 1:10

The term Liquor Ratio also conveys the same meaning, simply called as LR.

5. LIQUOR RATIO

It is defined as the ratio of the volume or the quantity of the liquor to be used to the weight of the material to be processed.

LR = Volume of Liquor / Weight of Textile Material

Example, LR = 50:1 means 50 Litres of Liquor for 1 Kg of material.

6. RETARDING OR LEVELLING AGENTS

In the dyeing process where the dyeing rate is very high, it is difficult to produce even shades or desired results. In such cases, the dyeing conditions are altered to decrease the rate of dyeing to get level dyeing results. For this purpose, dyeing assistants are added in the dye bath which gets combined with the dye to form a loose complex, which then cannot enter the fibre or fabric structure. However, this complex has to be broken subsequently, generally by raising the temperature so that the dye is again made available, but gradually for the dyeing process. Since, these dyeing assistants slow down the rate of dyeing and help to produce level dyeing results; they are called retarding agents or levelling agents.

7. EVEN DYEING

Even Dyeing resultsThe addition of retarding agents to slow down the dyeing process helps to produce even dyeing or level dyeing results, i.e., uniform dyeing without any patches and variations. Therefore, even dyeing is the desired end result of the dyeing process where no patches and variations or unlevel dyeing occurs.

8. SATURATION DYEING

If we go on increasing the % Shade of dyeing at certain depth, the fibre will get saturated with the dye and there will be no further increase in the depth, while the excess dye remains in the dye bath. This point where there is no further increase in transfer of dye molecules to the fibre and the depth of the shade remains constant even after continuing dyeing further, is called saturation dyeing.

9. RATE OF DYEING

It is the amount of dye transferring into the material per unit time.

10. APPARENT DEPTH

This is the actual depth (or shade) which you get after completing the dyeing process.

11. ON-TONE DYEING

When the tone of the fabric is not changing with time only depth increases or changes, it is known as on-tone dyeing.

12. % EXHAUSTION

Dyebath after exhaustion
Unexhausted Dye left in the dyebath after completion of Dyeing

The dye uptake of the fibre during dyeing is expressed in terms of % Exhaustion of the dyebath. It is the % of the amount of dye which actually goes into the fibre during dyeing from the initial amount of dye taken for dyeing. Thus if a dyebath contains ‘x gm/ltr’ of the dye before dyeing and ‘y gm/ltr’ at the end of dyeing, the % Exhaustion is given by

% Exhaustion = (x – y / x) X 100

Example, if 2 Kgs of dye is taken for dyeing and only 1 kg of dye actually transferred onto the fibre while the remaining 1Kg is left behind in the dye bath than it is said to have attained 50% Exhaustion.

13. % EXPRESSION OR % WET PICK-UP

It is the amount of liquor in gms carried by per 100gms of fabric after passing through the padding mangle, which is expressed as a percentage.

Example, when 1 Kg of fabric is padded on a mangle and after passing through the mangle if the weight of the fabric rises to 1.7 Kg. than the 0.7 Kg of liquor is than expressed as % to the initial weight of the fabric. Therefore in this case,

the % Expression = {(Final Wt of Fabric – Initial Wt of Fabric) / Initial Wt of Fabric} X 100

                                  = (1.7 Kg – 1 Kg / 1) X 100

                                  = 0.7 X 100

                                  = 70 %

14. % ADD ON

It is the term used to express the amount of a substance applied as its solution or dispersion after padding on a mangle, which results in weight gain of the final product after dyeing. In contrast to % Expression where the amount of liquor retained by the material after padding is expressed as percentage, here in % Add-on the amount of solid material giving extra weight gain to the material is expressed as a Percentage. Example, when size is applied to warp yarns; it is expressed as % Add-on. Also during finishing, when stiffeners and other add-on finishes are applied they are expressed as % add-on.

15. % OWM (On Weight of Material)

The amount of chemicals in gms to be used per 100 gm of material is called % OWM. Example, for 5% OWM Na2CO3, 5gms of Na2COis to be used per 100gm of material.

16. GPL (Grams per Litre)

The amount of chemical in gms to be used per one litre of liquor is called gpl. Example, for 40 gpl NaCl, 40gms of NaCl  is to be used per 1000ml of liquor.

17. COLOUR FASTNESS

It can be defined as the dye or colour present on the material after the dyeing process should not easily come out during washing. For different end-uses different fastness properties are required. Therefore the fastness of the dye depends on the tendency or the property of the dye to remain on the material during its end-use for which the material is intended for. There are several types of Fastness properties like Washing fastness, Light fastness, Rubbing fastness, Perspiration fastness, etc.

The dye is said to have an excellent washing fastness, when the depth and tone of the dyed material remains constant without bleeding and staining to adjacent materials even after several repeated washings.

LEAVE A REPLY