Basic Dye:
Basic dyes are called so since they are salts of organic bases. Basic dyes are also called cationic dyes because in solution the basic dye molecule ionizes, causing its colored component to become an action of positively charged radical. Basic dyes are used for dyeing wool, silk, and acrylic and mod-acrylic fibres.
Characteristics of Basic Dye:
Ø Ionic nature:-The ionic nature of these dyes is cationic.
Ø Shade range:- These dyes exhibit an unlimited shade range with high tinctorial strength, brightness and many colors are having fluorescent properties.
Ø Solubility:-The solubility of these dyes is very good in water ,in the presence of glacial acetic acid.
Ø Leveling properties:- These dyes have a very high strike rate , therefore leveling is poor.
Ø Exhaustion :- cationic dyes exhaust at a variable rates, K values are used to define the exhaustion characteristics of the cationic dyes. K=1 means the fastest exhaustion , while K=5 means the slowest exhaustion. So while making the combination shades the dyes of similar K values must be used.
Ø Affinity:- These dyes shows a very affinity towards wool , silk and cationic dye able acrylic, but have no affinity towards cellulosics. To dye cellulosics with basic dyes the material must be treated with suitable mordanting agents.
Fastness Properties:- The light fastness is poor to moderate , but wet fastness is good.
Dyeing of Acrylic with Basic Dyes
The most common anionic group attached to acrylic polymers is the sulphonate group, -SO3-, closely followed by the carboxylate group, -CO2-. These are either introduced as a result of co-polymerisation, or as the residues of anionic polymerisation inhibitors. It is this anionic property which makes acrylics suitable for dyeing with cationic dyes, since there will be a strong ionic interaction between dye and polymer (in effect, the opposite of the acid dye-protein fibre interaction).
Advantages of Basic Dyes
•High Tinctorial strength
•Moderate substantivity
•Relatively economical
•Wide shade range
•Includes some of the most brilliant synthetic dyes
•Shows good brightness
Limitations of Basic Dyes
*Poor shade stability
*High acid content
*Coloured backwaters
*Very poor lightfastness
*Preferential dyeing
Key advantages over conventional basic dyes:-
•Excellent substantivity
•Better Lightfastness
•Covers all fibres
•Clear backwaters
Properties of Basic Dyes
Ø The outstanding characteristics of the basic are brilliance and intensity of their colors.
Ø The bright colors achieved from basic dyes do not usually occur with other dye classes.
Ø Many of the basic dyes are sparingly soluble in water.
Ø The addition of glacial acetic acid helps to dissolve the basic dye quickly in water.
Ø Basic dyes are readily soluble in alcohol or mentholated spirit.
Ø The basic dyes are poor fastness to light and vary with regard to washing fastness from poor to moderate.
Ø An important property of basic dyes is that they will combine with tannic acid to form an insoluble compound provided mineral acid is absent.
Ø The wet fastness of the basic dyes on protein fibres can also be improved by back tanning. This consists of after treating the dyed material with tannic acid in order to form the insoluble complex thereby reducing the tendency to migrate.
Ø The basic dyestuff will combine with direct or sulphur or some acid dyestuffs. So they cannot be used together in the same bath. But basic dyestuffs are used in after treating cotton or other materials dyed with direct colors. Here the direct dyestuff acts as mordant.
Ø When treated with a reducing agent most of the basic dyes get converted into their colors less leuco compounds, return to their original color by oxidizing agents or even by exposure to air.
Ø Basic dyes can be removed from the material by boiling it with dilute acetic acid or hydrochloric acid.
Ø Basic dyes are used for woolen goods when particularly bright shades are required which cannot be obtained with an acid dyes.
Ø Basic dyes do not have affinity for cellulosic fibres like cotton. The use of basic dyes on cotton involves the troublesome process of mandating with tannic acid. But, sometimes, bright shades are demanded on cotton which can only be obtained with them.
Ø Special cationic dyes are available for dyeing acrylic fibres.
Ø Basic dyes are also used for making inks, typewriter ribbons and dyeing leather
