BASIC DYES:-
Basic Dyes:-
Properties, Classification of Basic dyes:-
Basic dyes are called so since they are salts of organic bases. They are also known as cationic dyes because of the presence of positive charge in the dye molecules under dyeing conditions. During dye application, the negatively charged acrylic fiber attracts the positively charged dye cations for ionic bonding. Due to high attraction between the oppositely charged fiber and dye molecules, there is risk of unlevel dyeing because of high rate of dyeing. This risk may be reduced by careful control of dyeing temperature and used of suitable retarding agents.
The basic dyestuffs are well known for their intense hues and brilliant shades, unrivalled by any other class of dyes. Basic dye has excellent light fastness because of their resistance to destructive effect of ultraviolet radiations in sunlight. Their washing fastness is also quite good, which may be attributed to hydrophobic nature of the acrylic fiber and good substantivity of the dye for the fiber. The basic dyestuff are most commonly used for dyeing polyacryonitrile or acrylic materials. Basic dye is also used for dyeing wool and silk fibers.
The general characteristic of a basic dye is the cationic group, which leads to formation of an ionic bonding to anionic groups present in the fiber polymer. Representative examples for basic dye are given in below Figure.
Figure: Representatives for basic dye: (a) C.I. Basic Red 1, (b) C.I. Basic Red 118, (c) C.I.
Basic Blue 41 and (d) C.I. Basic Blue 9 (Methylene blue).
The dyes contain polar groups for solubilising (e.g. amino groups); however, no sulphonate groups are present. A wide variety of chromophores is used in basic dye.
Basic/Cationic dyes are availble in:
1) Powders.
2) Pearls.
3) Liquids.
Characteristics/ Properties of Basic Dyes:-
1) The outstanding characteristics of the basic are brilliance and intensity of their colors.
2) The bright colors achieved from basic dyestuffs do not usually occur with other dye classes.
3) Many of the basic dyestuffs are sparingly soluble in water.
4)The addition of glacial acetic acid helps to dissolve the basic dye quickly in water.
5) Basic dye is readily soluble in alcohol or mentholated spirit.
6) The basic dyestuffs are poor fastness to light and vary with regard to washing fastness from poor to moderate.
7) An important property of basic dye is that they will combine with tannic acid to form an insoluble compound provided mineral acid is absent.
8) The wet fastness of the basic dye on protein fibers 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.
9)The basic dyestuff will combine with direct dyes or sulphur dyes 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.
10) When treated with a reducing agent most of the basic dye get converted into their colors less leuco compounds, return to their original color by oxidizing agents or even by exposure to air.
11) Basic dye can be removed from the material by boiling it with dilute acetic acid or hydrochloric acid.
12) Basic dye are used for woolen goods when particularly bright shades are required which cannot be obtained with an acid dyes.
13) Basic dye do not have affinity for cellulosic fibers like cotton. The use of basic dye 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.
14) Special cationic dyes are available for dyeing acrylic fibers.
15) Basic dyestuffs are also used for making inks, typewriter ribbons and dyeing leather.
Types/ Classification of Basic Dyes:-
The conventional basic dyes belong to several chemical classes, such as:
1) Diphenylmethane or ketone imine (presence of C=NH group), e.g. C.I. Basic Yellow 1.
2) Triphenylmethane, e.g. C.I. Basic Green 4, C.I. Basic Blue 5 and C.I. Basic Violets 3 and 14.
3) Thiazine (nitrogen and sulphur atoms forming a ring with benzene carbons), e.g. C.I. Basic Blue 9 and C.I. Basic Green 5.
4) Oxazine, similar to thiazine, but nitrogen and oxygen atoms form a ring with benzene carbons, e.g. C.I. Basic Blue 12.
5) Azine, similar to thiazine, but two nitrogen atoms form a ring with benzene carbons, e.g. C.I. Basic Red 5.
6) Xanthene (two benzene rings linked by oxygen atom and methylene bridge) derivatives, e.g. C.I. Basic Violet 10.
7) Acridine (two benzene rings linked by a nitrogen atom and –CH= group) derivatives, e.g. C.I. Basic Orange 14.
8) Azo groups, e.g. C.I. Basic Brown 1.
Advantages of Basic Dyes:-
1) High Tinctorial strength.
2) Moderate substantivity.
3) Relatively economical.
4) Wide shade range.
5) Includes some of the most brilliant synthetic dyes.
6) Shows good brightness.
Limitations of Basic Dyes:-
1) Poor shade stability.
2) High acid content.
3) colored backwaters.
4) Very poor lightfastness.
5) Preferential dyeing.
Modified Basic Dyes:-
These dyes, generally based on the chemistry of basic dyes, have longer molecular structures than traditional basic dye, and thus have significantly improved properties.
Though still cationic in nature, modified basic dyestuffs exhibit improved fiber coverage and substantivity on many furnishes, making them ideal for dyeing applications. Lightfastness is also improved considerably over traditional basic dye.
Key Advantages Over Conventional Basic Dyes:-
1) Excellent substantivity.
2) Better Lightfastness.
3) Covers all fibers.
4) Clear backwaters.
Application of the Basic Dyes:-
Basic dyestuffs are extensively used for dyeing of jute, cut flowers, dried flower, coir, etc. For dyeing Acrylic fibers, basic dye are used widely. Modified basic dye is used for dyeing of Acrylic fiber, because these are perfect for this material. If the reason behind the success of Basic dyes is analysed, it would be seen that the positively charged cations of the Basic dyes gets attracted towards the negatively charged anions in the acrylic fiber. Acrylic polymers have anionic groups attached to it. They are most commonly the sulphonate group, –SO3−, followed closed by the carboxylate group, –CO2−. This reaction of the cation and anion results in salt linkages. Basic dye does not show absolutely any migration in acrylic fibers under normal dyeing conditions.
Basic dyestuffs are also preferred to dye leather, because they can get combined easily with vegetable-tanned leather thus doing away with mordant. Basic dyes are also used in the coloring of papers. Basic dyestuffs for paper widely used in textile industries. Basic dye offered by us are used mainly in the applications of acrylic fibers such as types 42 and 75 orlon and type 61 creslan. The dye is generally used to produce bright and deep shades with superior light and wash fastness. Its application is similar to that of direct dyes but requires different and more precise controls with auxiliaries and temperatur.
Ref:-https://textilelearner.net
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