Technology of soaping: for quick removal of reactive dyestuff
Takashi Kotani, President
2. Recent studies
The common trend in research and studies on this reactive-dyestuff soaping, still actively carried out in Europe and the US, is to analyze the amount of wash-out at each soaper by using equipment simulating the actual production process. Temperature and time for hot/cold rinsing after dyeing and post-printing steaming are observed, as well as the process speed and rates of dyestuff removal in relation to the bath ratio. The point of these studies is to achieve a rational soaping process on a large scale by using a technology that incorporates the following practical factors:
1) Saving water, energy and time
2) Realizing a smart process with quick soaping in a small bath ratio
3) Standardizing control system and reducing cost of production
4) Controlling and reducing waste water for protection of the environment |
More specific studies are listed below.
Wash-off properties can be affected by temperature difference between mono-functional and bi-functional dyestuff during continuous soaping.(1)(4)
Hot rinsing can be very effective in washing off unfixed and hydrolyzed dyestuff especially in the case of high affinity, and an observation of the effectiveness according to temperature, the relationships between pH, salt concentration and flow rate has been carried out, parametrically indicating optimum rinsing and soaping after package dyeing.(3)
Aspland(2) suggests, for the setting of appropriate conditions and temperature, that it is preferable to begin with hot rinsing for the removal of unfixed and hydrolyzed dyestuff which carries a high affinity, though he also points out extreme temperatures and high/low pH often cause discoloration due to hydrolyzing of dyestuff.
Thomsen(5) indicates in his graph that the possibility of removal of more than 50% of the total amount of washed-off dyestuff coming from hydrolyzed dyestuff with high affinity through hot rinsing at a high temperature between 70 and 95°C.
G. L. Bhalla(6) indicates alkali hydrolyzed in soaping through the use of a SN2 mechanism of nucleophilic displacement reaction to describe the condition of transition and sectional bond of dyestuff.
Kotani(7) discusses the appropriate use of a soaping agent for setting optimum soaping conditions and preventing staining of white ground.
The above recent studies mostly deal with the use of appropriate temperature for soaping. |