1. Preface
(b) Inactive, unfixed dyestuff
(c) Hydrolyzed dyestuff produced in the presence of water and alkaline or acid
2. Recent studies
(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.
3.Characteristics and performance
Originally, the goals of reactive-dyestuff soaping are:
●the removal of unfixed dyestuffSetting of a high temperature seems preferable for removal, however, washed-off dyestuff often diffuses and penetrates into the yarn, resulting in re-adsorption and staining.
Moreover, it is not easy to achieve complete, quick soaping on printing paste since the concentration of dyestuff and the amount of paste deposition are high. Thus, the use of a special soaping agent, capable of producing maximum effects in a quick strong soaping at a small bath ratio, while preventing redeposition and staining of white ground regardless of rinsing temperature or any difference in process conditions, is considered most rational.
Though multiple soaping agent structures have been made public so far, it is very difficult for a single chemical structure to satisfy the above description. Fig. 1 shows some interesting chemical structures that are not only restricted to the idea of using surfactants as the base.
4. Emill
An optimum soaping agent for reactive dyestuff will require:
Group (A) |
G-170, G-100 and G-50 potently prevent redeposition of wash-off and staining besides removing it. White-ground soaping agents suitable for prints. Versatile and inexpensive. |
Group (B) |
2G conc, 2G conc new and BZ conc are conc-type products with superior soaping properties and good stain removal. |
Group (C) |
R-60, YK and 2G can balance the performance between wash-off removal and prevention of staining (the characteristics of A and D). Most conventional, versatile and inexpensive products. |
Group (D) |
Powerful soaping with anti-staining/redeposition properties, outstanding effects in the removal of staining 5G conc. SK-D: Also suitable for deep-printing G-A: Good for deep-dyeing (black) |
Table 1 is the summary of the performances, purposes and characteristics of above products. Table 1 Emill group characteristic, performance and method
When dyeing only the cotton side of polyester/cotton union cloth (border pattern) with reactive black dyestuff (VS type), the polyester side becomes stained and is no longer available for reserve dyeing. The graph in Fig.2 shows that the amount of reactive dyestuff remaining on the polyester part and the amount of unfixed dyestuff on the cotton after soaping this one-side dyed material at 60°C, 75°C and 90°C.
In ②, the high-temp (90°C) rinsing removed more than 50% of unfixed dyestuff on the cotton part without using any soaping agent, but it proved impossible to remove the stain on the polyester.
In ③ and ④, a competitor's soaping agent was added. Removal of stains on polyester was incomplete, without any improvement observed even with the use of STPP (sodium tripolyphosphate).
In ⑤ and ⑥, EMILL SK-D was used. Deposition on both fibers was removed effectively with soaping above 75°C. The addition of STPP proved effective and brought about improved results.
Fig.3 shows comparison of anti-staining effects and colorfastness to washing according to the kind of soaping agent in 60°C, 75°C and 90°C soaping of reactive-dyed cotton.
Soaping was carried out directly after dyeing 100% cotton knit with C. I. Reactive Red 120, without undergoing cold or hot rinsing. To test the anti-staining of white ground, stains on white cloth were observed with a white cloth added to the soaping bath. To test fastness to washing, bleeding on an attached white cloth was measured after the soaping and drying of a dyed cloth, using the launderometer, based on JIS A-4 method.
② is a conventional type with a balance between removing and anti-staining properties.
③ causes no staining on white ground because of low removing properties and has very low fastness to washing.
④ is potent in removal but inferior in preventing staining, resulting in more redeposition of dyestuff and low washing fastness.
As described above, the performance of soaping agents differ according to the kind. Emill G-170 (⑤) has a very low concentration of 0.5 g/L and shows great results in both anti-staining of white ground and washing fastness.
Test method
Dyeing of cotton cloth with CI Reactive Black 5
→Soaping (80°C x 10min) and drying
→The dyed cloth and cotton white cloth sewn together vertically
→The bottom of the dyed cloth dipped in a 0.5g/L solution of nonionic surfactant, 20°C x 10min.
→Determination of the bleeding rate of the reactive dye remaining unfixed on the white cloth
5. Conclusion
References:
(2) Aspland: Tex chemist & col 24 (5) 36 (1992)
(3) Technical paper: Tex chemist & col 23 (No11) 21 (1991) 23 (No1) 13 (1991)
(4) Luttringer: Textilveredlung 25 (No10) 313 (1990)
(5) Thomsen: Mell Textilber 75,220, 3 / 1994
(6) G. L. Bhalla: Am Dyestuff Repter 81, (No7) 38 (1992)
(7) Kotani: Dyeing & Finishing 46 (No13) 693 (1994)
(8) CA 115 (18) 185801w
(9) CA 121 (22) 258574k
(10) CA 98 (10) 74296w
(11) CA 93 (4) 27692j
(12) CA 109 (26) 232705f
(13) CA 114 (26) 249244f
(14) CA 90 (26) 206270e