Disperse Dye

Disperse dye is originally developed for the dyeing of cellulose acetate. They are substantially water insoluble. The dyes are finely ground in the presence of a dispersing agent then sold as a paste or spray dried and sold as a powder. They can also be used to dye nylon, triacetate, polyester and acrylic fibres. In some cases a dyeing temperature of 130 deg C is required and a pressurized dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.

Disperse dyes have low solubility in water, but they can interact with the polyester chains by forming dispersed particles. Their main use is the dyeing of polyesters, and they find minor use dyeing cellulose acetates and polyamides. The general structure of disperse dyes is small, planar and non-ionic, with attached polar functional groups like -NO2 and -CN. The shape makes it easier for the dye to slide between the tightly-packed polymer chains, and the polar groups improve the water solubility, improve the dipolar bonding between dye and polymer and affect the colour of the dye. However, their small size means that disperse dyes are quite volatile, and tend to sublime out of the polymer at sufficiently high temperatures.

The dye is generally applied under pressure, at temperatures of about 130oC. At this temperature, thermal agitation causes the polymer's structure to become looser and less crystalline, opening gaps for the dye molecules to enter. The interactions between dye and polymer are thought to be Van-der-Waals and dipole forces.

The volatility of the dye can cause loss of colour density, and staining of other materials at high temperatures. This can be counteracted by using larger molecules or making the dye more polar (or both). This has a drawback, however, in that this new larger, more polar molecule will need more extreme forcing conditions to dye the polymer2.

The most important class is the azo class. This class of azo disperse dyes may be further sub-divided into four groups, the most numerous of which is the aminoazobenzene class. This class of dye can be altered as mentioned before, to produce bathochromic shifts. A range of heterocyclic aminoazobenzene dyes are also available. These give bright dyes, and are bathochromically shifted to give blues. The third class of disperse dye is based on heterocyclic coupling components, which produce bright yellow dyes. The fourth class are disazo dyes. These tend to be quite simple in structure. Other than these, there are disperse dyes of the carbonyl class, and a few from the nitro and polymethine classes.

Common and Generic Names for Disperse Dyes

Colour Index Names for PROSperse Disperse Dyes

PRO chem # Name Colour Index Name

D118 Bright Yellow        Disperse Yellow 218 D225 Clear Orange Disperse Orange 25 D333 Fuchsia Disperse Violet 33 D350 Flame Scarlet Disperse Red 325 D360 Bright Red Disperse Red 60 D426 Turquoise Disperse Blue 26 D450 National Blue Disperse Blue C-4RA (manufacturer's mix?) D459 Bright Blue Disperse Blue 56 D460 Deep Navy Disperse Navy 35 D650 Cool Black Disperse Black C-MDA (manufacturer's mix?) D770 Meadow In House Mix D773 Sage In House Mix D880 Iris In House Mix D885 Lilac In House Mix D125 Buttercup In House Mix

APPLICATION OF DISPERSE DYES:

Dyeing Polyester with Disperse Dyes

Polyester requires the use of disperse dyes. Other types of dyes leave the color of polyester almost entirely unchanged. While novices happily charge into dyeing with acid dyes (for wool or nylon) and fiber reactive dyes (for cotton and rayon), often with excellent results, the immersion dyeing of polyester is a different story. However, disperse dye can be used by even young children to make designs on paper, which can then be transferred to polyester fabric, or other synthetics, with a hot iron. The possibilities are endless, using fabric crayons, rubber stamps, painting, and even screen printing.

Stamp Pad Ink

Disperse dye can be applied to paper with rubber stamps, and then ironed on to polyester, just like the crayons. You can use special, large-scale fabric stamps to apply other dyes to fabric, but only disperse dyes allow such fine lines that almost any rubber stamp designed for use on paper will work, if your fabric is smooth enough. Look for a product called "Heat Set Ink" at companies that sell rubber stamping supplies. Caroline Dahl's wonderful book Transforming Fabric gives source information for this material, in addition to many project ideas and beautiful inspiring photographs of works made with disperse dye on polyester.

PROPERTIES OF DISPERSE DYE:

Fastness to light is generally quite good, while fastness to washing is highly dependent on the fibre. In particular, in polyamides and acrylics they are used mostly for pastel shades because in dark shades they have limited build-up properties and poor wash fastness.

Chemical characteristics and general application conditions

Disperse dyes are characterised by the absence of solubilising groups and low molecular weight. From a chemical point of view more than 50 % of disperse dyes are simple azo compounds, about 25 % are anthraquinones and the rest are methine, nitro and naphthoquinone dyes.

The dye-fibre affinity is the result of different types of interactions:

· hydrogen bonds

· dipole-dipole interactions

· Van der Waals forces.

Disperse dyes have hydrogen atoms in their molecule, which are capable of forming hydrogen bonds with oxygen and nitrogen atoms on the fibre.

Dipole-dipole interactions result from the asymmetrical structure of the dye molecules, which makes possible electrostatic interactions between dipoles on the dye molecules and polarised bonds on the fibre.

Van der Waals forces take effect when the molecules of the fibre and colourant are aligned and close to each other. These forces are very important in polyester fibres because they can take effect between the aromatic groups of the fibre and those of the colourant.

Disperse dyes are supplied as powder and liquid products. Powder dyes contain 40 - 60 % of dispersing agents, while in liquid formulations the content of these substances is in the range of 10 - 30 %. Formaldehyde condensation products and ligninsulphonates are widely used for this purpose.

Dyeing with disperse dyes may require the use of the following chemicals and auxiliaries:

· dispersants: although all disperse dyes already have a high content of dispersants, they are further added to the dyeing liquor and in the final washing step

· carriers: for some fibres, dyeing with disperse dyes at temperatures below 100 °C requires the use of carriers. This is the case with polyester, which needs the assistance of carriers to enable an even penetration of disperse dyes below boiling temperature. Because of environmental problems associated with the use of these substances, polyester is preferably dyed under pressure at temperature >100 °C without carriers. However, carrier dyeing is still important for polyester-wool blends, as wool must not be submitted to wet treatment at temperatures significantly above 100 °C

· thickeners: polyacrylates or alginates are usually added to the dye liquor in padding processes. Their function is to prevent migration of the dye liquor on the surface during drying

· reducing agents (mainly sodium hydrosulphite): they are added in solution with alkali in the final washing step.

Disperse dyes are widely used not only for dyeing, but also for printing synthetic fibres.

Environmental issues:

The environmental properties of disperse dyes are assessed under the following parameters

Parameters of concern

Comments

Bio-eliminability Owing to their low water-solubility, they are largely eliminated by absorption on activated sludge in the waste water treatment plant

Organic halogens (AOX)

Some disperse dyes can contain organic halogens, but they are not expected to be found in the effluent after waste water treatment (because they are easily eliminated by absorption on the activated sludge) (see also Section 2.7.8.1)

Toxicology The following disperse dyes potentially have an allergenic effect: Disperse Red 1, 11, 17, 15; Disperse Blue 1, 3, 7, 26, 35, 102, 124;Disperse Orange 1, 3, 76; Disperse Yellow 1, 9, 39, 49, 54, 64.

Heavy metals

Aromatic amines These dyes are still offered by some Far East dealers and manufacturers [294, ETAD, 2001]

Unfixed colourant Level of fixation is in the range of 88 - 99 % for continuous dyeing and 91 - 99 % for printing

Effluent contamination by additives in the dye formulation

Conventional dispersants (formaldehyde condensation compounds, lignosulphonates, etc.) are poorly biodegradable (<30 % according to [186, Ullmann's, 2000], ca. 15 % according to [18, VITO, 1998]). Some dyes are formulated with more readily eliminable dispersants (albeit not suitable for all formulations). More information is reported in Section 4.6.3

Classes of disperse dye:

Azo Disperse Dye:

The most important class of disperse dye is the azo class.  This class of azo disperse dyes may be further sub-divided into four groups, the most numerous of which is the aminoazobenzene class.  This class of dye can be altered as mentioned before, to produce bathochromic shifts.  A range of heterocyclic aminoazobenzene dyes are also available.  These give bright dyes, and are bathochromically shifted to give blues.  The third class of disperse dye is based on heterocyclic coupling components, which produce bright yellow dyes.  The fourth class are disazo dyes.  These tend to be quite simple in structure.  Other than these, there are disperse dyes of the carbonyl class, and a few from the nitro and polymethine classes.  Below is an example of a disperse dye2

Anthraquinone Disperse Dye:

Anthraquinone disperse dyes lack the water-solubilizing groups of the acid dyes, but they are adsorbed by hydrophobic fibres such as nylon or acetate rayon with the aid of soap or other agents that keep the dye suspended in the application bath.

In the synthetic dye field, many hundreds of individual products are manufactured. Of these, a small number become established as market leaders in their particular area of utility. Factors influencing the attainment of this status by a particular dye include hue, brightness, ease of manufacture, dyeing properties and fastness properties. One dye that has reached this position for the production of blue shades on polyester fibers is CI Disperse Blue 56 which has a simple anthraquinone structure and is easily applied giving bright blue colorations of high fastness.

Dyes of the anthraquinone series are noted for their brilliance of hue, especially in the blue region, and also for their excellent fastness properties, especially fastness to light. Unfortunately, they have relatively low tinctorial strength compared with all other major classes of dye and they are costly to manufacture. The replacement of anthraquinone dyes by other chromophores, because of their low cost-effectiveness, has been described by Renfrew (Rev.Prog.Coloration, 15, 1985, 15) as "a commercially attractive but technically difficult objective for dye manufacturers".

Thiocyanomethyl substituted anthraquinone disperse dyes

The present invention relates to disperse dyestuffs of the anthraquinone series which contain at least one group of formula --Y--CH2 (SCN) where Y is a mono- or binuclear aryl group, which dyestuffs are useful for dyeing or printing textile substrates consisting of or comprising synthetic or semi-synthetic, hydrophobic high molecular weight organic materials.

Light fastness:

The photofading behaviors of anthraquinone disperse dyes on polylactide fabrics were investigated. The fabrics which had been dyed with 13 commercial dyes were exposed to a carbon arc light source. The polylactide fabrics dyed with Disperse Red 127 or Violet 26, which have phenoxy substituents, showed the light fastness higher than 4 grade.