Saminathan Ratnapandian

Equipment

1. Padding mangle, steamer and dryer

The equipment described in Sections 3.2.1, 3.2.2 and 3.2.3 was used for padding, steaming and drying. Steaming was carried out using saturated steam at 100^○C and 100% RH. Various steaming durations were employed as indicated in later sections. The drying temperature was 65^○C.

2. Printing

A Tiffany brand hand mixer (model number HM218) was used for blending the print paste. Table-top printing, simulating a 48T screen mesh, was achieved by employing a combination of a K-Bar hand coater and a number 2 (two) K-Bar (RK Print Coat Instruments), shown in Figure 6.1. The precision-wound steel-wire construction of the K-Bar allows only a specific quantity of print paste to be spread on a sample. This eliminates process variations such as squeegee pressure and quantity of print paste, the outcome being consistency and repeatability of the printing trials [198].

Figure 6.1 K-Bar hand coater [198]

3. Materials

Cotton fabric and indigo (natural and synthetic) as described in Section 2.2.1.1 and Section 2.2.1.2 were used in the experiments. Table 2.2 lists the other chemicals utilised in the recipes.

4. Methods

   1. Indigo dyeing

Exhaust method
As a benchmark, cotton fabric was dyed using indigo (natural or synthetic) to a 1.5% depth of shade on the weight of material (OWM) according to the recipe and process suggested by Kraftkolour, the indigo dye supplier. A material-to-liquor ratio of 1:30 was used. Table 6.1 lists the constituents of the dye bath. The dye was dissolved (dispersed) using 30% of the calculated volume of water (at 35^○C) resulting in a blue solution. The calculated amounts of sodium dithionite, sodium hydroxide and dextrose were added to this solution and mixed thoroughly. Dextrose, a reducing agent by itself, lowers the oxidation rate of sodium dithionite and served as a stabiliser for the reducing agent. The remaining 70% of water (at room temperature) was added and the dye solution was left undisturbed for 20 minutes to permit complete reduction (vatting) of the indigo. This was indicated by change of the solution colour from blue to pale yellow.

Table 6.1 Indigo exhaust dyeing recipe