 |
|||||||||||||||||||||||||||||||
Bifunctional dyes:The following procedure is most suitable for a soft-flow and jet type of dyeing machines, where effective water and fabric circulation is possible. The starting dye bath pH is set between 5.5 and 6.5 by using adequate quantity of Acetic acid. A general recipe for obtaining best results in the reactive dyeing process with a water of minimum hardness will be:
What are bifunctional dyes?:
Recently dyes have become available which have both type of reactive group. The question is, what might these bi- and poly-functional dyes be able to do that mono-functional reactive dyes cannot? The answer depends on three factors: probability of fixation, relative color efficiency and dye bath behavior. The bifunctional dyes have more migration and fixation properties than its counter part Vinylsuplones. Since there are two reactive ends the bath exhaustion will be more than Vinylsulphone dyes. These dyes exhibit a total exhaustion/fixation of 85% to 90% as against the conventional Vinylsulphones where the exhaustion/fixation would be around 60% only. The higher fixation leads to less colored discharge in the effluent. The application part of bifunctional dyes is purely dependent on the construction of the textile fabric, processing machinery available and the difficultly of the shade to be dyed. All these things to be taken care of by a qualified Textile Dyeing Technician. DYEING GUIDE LINES/GENERAL PARAMETERS: HOT PROCESS – CHEMICAL REQUIREMENTS:
This is a versatile method suitable for all kinds of well absorbent fabrics.
This method is effective for retarding initial dye adsorption and improving dye migration and also for swelling fibers to improve dye penetration. This method is therefore suitable for dyeing densely loaded materials, mercerised cotton and viscose rayon. Washing & Soaping Procedures: The unfixed dye, excess alkali and salt has to be removed by 1 to 2 cold rinses followed by a neutralization with 1 g/l of Acetic acid in cold condition. The washing/Rubbing fastness of very dark shades can be improved by a warm wash (50°C), followed by 2 cold washes before neutralization. After neutralization, do one cold wash followed by non-ionic soaping (1 –2 g/l) at boil for 15 minutes. Then rinse in warm water followed by cold wash. After Treatments: Normally a thorough soaping and washing will eliminate all hydrolyzed unfixed dyes from the fabric and ends in good washing and rubbing fastness. A softening treatment with cationic or silicone softener may be carried out according to the requirement.
Note: In practice, there are possibilities of mixing two classes of reactive dyestuffs viz., a) Bi-functional dyes and Vinylsulphone dyes b) b) Bi-functional and Cold brands c) c) Bi-functional and High Exhaust Though, strictly speaking these mixtures may create a lot of reproducibility and application problems, an adept dyer can manipulate and achieve good results. When making such mixtures, one should take care of the dyeing/fixation temperatures, the alkali requirements, the time durations necessary etc. Generally dyestuff manufacturers do not recommend for dyeing with mixed alkali methods, because except a few dyestuffs, all others will yield a lower depth and poorer wash & rub fastness results. We recommend use V.S. dyes for producing bright greens and turqs. The dissolving of Bi-functional dyes is a crucial step, which determine the color yield, repeatability and lab to bulk reproducibility. 1. If the shade we are going to be dyed is a tri-chromatic one, i.e., a combination of three dyes, each dyestuff in the combination should be weighed separately and put into separate containers. 2. Each dye should be dissolved separately using 1:15 MLR ratio i.e., for 1 kg of dye 15 liters of water should be used. 3. First the dye should be pasted thoroughly, with a little cold water into a uniform colloidal mass. Then add hot water of 85°C and dilute. 4. Filter through fine bolting cloth and the mix the three dyes. 5. Do not add urea directly to the solid dye powder. If large quantities Of dyestuff is dissolved, add 1/10th by weight of urea to dissolved solution to improve dissolution.
Sampling/Shading procedure/Addition of Dyes during dyeing: 1. Do not compare any sample taken just after the addition of salt against the standard shade. This will mislead you. 2. Take sample 30 minutes after the addition of soda for light & medium shades and 45 minutes for dark and v.dark shades. 3. Wash Cold- ½ minute 4. Wash Hot – 60°C- ½ minute 5. Neutralize – cold- ½ minute with 1 g/l acetic acid. 6. Neutral soap – boil – ½ minute 7. Neutral soap – boil – ½ minute 8. For dark and v.dark shades, do 6 soaping’s of ½ minute duration. 9. Cold wash. 10.check shade. 1.If shade is not matching, and if you want to make 10 or 20 or 30% addition in total, drain the running bath up to ½ volume, refill with fresh water, then add the required dye (pre-dissolved, filtered) in two portions, continue dyeing for another ½ half. Do not make any addition of salt or soda into the bath. After Treatments: 1. After dyeing is over, drain the bath. 2. Do one cold wash – no running bath. 3. Do one hot wash - 60°C – 10 minutes. 4. Do neutralization with 1 to 2 g/l of Acetic Acid. 5. Do one cold wash. 6. Neutral soap 0.5 to 1.0 g/l at 80 to 90°C for 15 minutes. 7. Hot wash at 80°C – 10 minutes. 8. Cold wash – 10 minutes. 9. Softening treatment with some non-ionic softener.
Printing: All Bi-functional dyes can be used for printing as well. A tentative print recipe for printing followed by steaming is as under. Dyestuff = x parts Urea = 100 parts Hot water = 250 parts 4% sod.Alginate = 570 parts Resist salt = 10 parts Sod.Bicarbonate = 20 parts Total = 1000 parts. Print, dry, steam in star ager for 15 minutes at 105°C. The material is rinsed cold, then hot. Neutralize with 1 g/lit of Acetic acid. Soap at boil with 2 g/l of Non-ionic detergent. Rinse cold and hot. *For Soft/Jet Flow type high speed Machines only. **. For water with more than 200ppm of Bicarbonates. Color Index Number, Fastness Properties and Discharge ability of Bi-functional dyes Best Trichromatic combinations - some tips
.
|
|
||||||||||||||||||||||||||||||
