Industrial Direct Dyes
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- Courier
- In detail
- Give fastness properties without after treatments
- By after treatments with copper compounds, the fastness to light can be improved in the case of sum direct dyes
- The fastness to light varies from very poor (class I) to out standing (class VIII)
- All direct dyes contain one or more sulphonic group in the form of sodium salt to impart water solubility and are AZO dyes
- Most of direct dyes, contain two or three AZO groups
- These are one of the most important groups of dyes due to its simplicity of application, availability in multiple shades and hues in a single class and its comparative cheapness
- Many of the direct dyes are dis-chargeable
- Matching specific shades of colors is easy as compared to other classes of dyes
Details of Dyeing (Direct Dyes)
First the colors of dyestuffs are pasted with cold water and then boiling water is added whilst stirring. The range of direct dyes is applied in baths that is neutral and does not contain acid, alkali & reducing or oxidizing chemicals. The dyeing is carried out at near to boiling temperature along with glober salt in baths that are neutral or weakly alkaline (soda-ash). Direct Dyes are primarily used to dye cotton, viscoss, cupramonium rayon and other such cellulose fibers using some special procedure.
In order to dye Nylon, at 40-90°C temperature the selected Direct Dyes are used with sulphate or Acetic Acid or Ammonium Acetate for about 60-90 minutes and then it is rinsed well. While in case of dyeing paper, before adding rosin and alum, pre dissolved Direct Dyes are added to paper pulp in the Beater.
Pre Treatments (Cellulose Material):
Pre Treatments are done on cellulose material to obtain level dyeing and enhance the brightness of any shade. The cellulose material should be void of any kind of impurities for penetration of dyestuffs while treating in boil bath that contains caustic soda detergent. It is taken in use for Dyeing after boiling it up to half an hour and then properly washed in cold water.