Dye application; dyeing control methods in continuous dyeing

Application of dyes in continuous dyeing process:

Dyeing is very important part of readymade garments manufacturing. The proper application of fashion in textile is totally depends on the types of dyeing. The proper shade matching is depend on the proper application of dyes. In continuous dyeing the quantity of dye applied to the textile fabric can be measured indirectly from the amount of moisture (liquor) applied dyeing machine by the padder (e.g. by means of microwaves). It would be even better, however, to measure the quantity of dye applied to the running fabric by taking reflection measurements on the wet fabric shortly after it leaves the dyeing machine padder nip since in this case it would be possible to make any necessary corrections from direct readings and the short control loop. Other control possibilities opened up by reflection measurements on the wet fabric include:

1. Concentration distribution of dyes and dyes chemical auxiliaries applied from the pad liquor (side. centre, side).

2. Localized dye pick-up of dyeing liquor by tile fabric (in relation to its dry weight before padding).

3, Localized residual moisture content of tile fabric entering tile liquor and tile exchange coefficient between water and product.

It is to be understood in this case that tile directly measurable dye pick-up parameter desired does not have to be replaced by a group of dye measurement parameters which can, ill principle, be handled but which require very involved measurements (the exchange coefficient is likewise not amenable to direct measurement. However, since it is only used as a correction parameter it can be applied as a value capable of interpolation from a series of trials).

Before a decision is made to invest in an elaborate measuring system of this kind for a particular process stage, it is of course necessary to establish first of all whether or not sufficient control would be achieved by measuring the dyed result at the end of the dyeing process and only then make any necessary corrections to the two factors exercising the greatest influence on the process. i.e. the dye liquor itself and the dye liquor pick-up. Color measurement on fabrics at the point of delivery from a continuous dyeing plant with a drier is state-of-the-art technology. Measuring sensors are already available which can take reflection measurements across the full width of dyed fabrics (by means of a single traversing measuring head or 3–5 dixed measuring heads) and display from the standard. The main problem here lies in the time response of the control system rather than in the measuring sensors. Measurements of dyeing are carried out approx. 30–100 m after the point of dye application. There is consequently a long time lag, i.e. under these conditions, many metres of fabric have to pass through the dyeing plant or dyeing machine after a correction has been made to the dye pick-up before the point of change in the fabric reaches the measuring head.

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