We bring a wide range of finest quality
acid dyes, which offer high wash fastness and color quality. These dyes are
water-soluble anionic dyes, which are applied to fibres such as silk, wool,
nylon & modified acrylic fibres from neutral to acid dye baths. Our acid
dyes are widely used to provide dyeing solutions on wool, other animal
fibers, and some manufactured fibers.
Acid dyes are water soluble anionic dyes that are applied to fibres such as
silk, wool, nylon and modified acrylic fibres from neutral to acid dye
baths. Attachment to the fibre is attributed, at least partly, to salt
formation between anionic groups in the dyes and cationic groups in the
fibre. Water soluable Acid dyes are not substantive to cellulosic fibres.
Acid dyes are used both commercially and by the studio dyer to dye
protein/animal fibers such as wool, silk, mohair, angora, alpaca and some
nylons and synthetics. Acid dyes require the use of an acid such as vinegar,
acetic or sulphuric acid to set the colour.
Acid dyes sound scary to some novices, who imagine that the dyes themselves
are caustic strong acids. In fact, the dyes are non-caustic, are in many
cases non-toxic, and are named for the mild acid (such as vinegar) used in
the dyeing process, and for the types of bonds they form to the fiber. Some
of them are significantly more toxic than fiber reactive dyes, while others
are even safe enough to eat, and are sold as food coloring.
- Leveling acid or strong acid dye,
- Milling or weak acid dyes, and
- Super milling or fast acid or neutral acid dyes.
Leveling Acid Dyes have been sold under the trade names of Kiton, Erio,
Intracid, Sandolan, and Amacid, among others; they are also the acid dye
component of all-purpose or union dyes such as Rit and Tintex, says Knutson.
It's difficult now to find out which specific acid dyes fall into which of
these dye classes, however. At least part of the reason is that the
information is not particularly useful to the dyer.
Most histologic dyes are classified either as acid or as basic dyes. An
acid dye exists as an anion (negatively charged) in solution, while a basic
dye exists as a cation (positive charge). For instance, in the
hematoxylin-eosin stain (H&E), the hematoxylin-metal complex acts as a
basic dye. The eosin acts as an acid dye. A very large class of dyes
containing acidic groups, such as the sodium salts of sulfonic acids or
phenolic groups. They are more soluble and have less tinctorial value than
basic dyes but they also have greater light fastness. They do not form lakes
with tannin. Acid dyes are used in dyeing leather, paper, etc., and their
particular value lies in their ability to produce brighter, more uniform
colours. They are normally applied from an acid dye liquor (acetic, formic,
or sulphuric acid); however, unless applied from a neutral or only slightly
acid dyebath, i.e., pH of 6.0 to 7.0, their use is likely to result in acid
degradation of the material dyed.
Direct dyes are another class of dyes,
one of the two types of dyes that are mixed in 'all purpose' dyes such as
Rit. (The other type in the mixture is an acid dye, which will not stay in
any cellulose fiber for long.) The colours of direct dyes are duller than
those provided by fiber reactive dyes, and the washfastness is poor - expect
anything dyed with them to 'bleed' forever. The one advantage is that direct
dyes may be more lightfast, that is, resistant to fading in the light, than
fiber reactive dyes. The "direct dye" classification in the Colour
Index system refers to various planar, highly conjugated molecular
structures that also contain one or more anionic sulfonate group. It is
because of these sulfonate groups that the molecules are soluble in water.
Though most direct dyes still can be obtained in powder form, it is
increasingly popular to receive them as liquid concentrates. The advantage
of concentrates is that they are easy to handle and meter. The disadvantage
is that the surfactants and co-solvents needed to keep the dye concentrates
stable may interfere with retention and sizing in the case of very deeply
coloured grades.
Direct dyes are used on cellulose fibers such as cotton, rayon, and linen.
They lack the permanence of the cold water fiber reactive dyes which most
serious dyers prefer for use on cellulose fibers, but in some cases they
have advantages that make their use worthwhile. For example, while many of
the direct dyes are not very lightfast, there are some dyes in the class
that may be more lightfast than similar shades of fiber reactive dyes. All
direct dyes perform rather poorly with respect to washfastness. Without an
appropriate after-treatment, direct dyes bleed a little with every washing,
losing their brightness and endangering other clothes washed in the same
load. However, there are special after-treatments which may be used to solve
this problem. (Vinegar is not among them! In spite of claims you may see to
the contrary, you cannot use vinegar to set any dye on cotton or other
cellulose materials.) A product called Retayne, which is an ionic bulking
agent which essentially "glues" the dye into the fiber, works very
well to make fabric dyed with direct dyes washable without bleeding of the
dye.
The name 'direct dye' alludes to the fact that these dyes do not require
any form of 'fixing'. They are almost always azo dyes, with some
similarities to acid dyes. They also have sulphonate functionality, but in
this case, it is only to improve solubility, as the negative charges on dye
and fibre will repel each other. Their flat shape and their length enable
them to lie along-side cellulose fibres and maximize the Van-der-Waals,
dipole and hydrogen bonds. Below is a diagram of a typical direct dye. Note
that the sulphonate groups are spread evenly along the molecule on the
opposite side to the hydrogen bonding -OH groups, to minimize any repulsive
effects.
