**Temperature**

The adsorption and diffusion of disperse dyes on polyester are greatly influenced by temperature as an increase in temperature increases the mobility of the polymer chains in the amorphous regions of the fibre. Polyester fibres dye very slowly at temperatures much below 100C. At 85C, the temperature normally used for the dyeing of secondary cellulose acetate, it was found that polyester fibre dyed at rates between 700 and 1000 times slower than those measured for the same dyes on secondary cellulose acetate and nylon (Nunn, 1979). When, however, sufficient time was allowed for the polyester fibre to come nearly to equilibrium with the dyebath, it was found that it had taken up approximately the same amount of dye as had secondary acetate and in most cases about twice as much as nylon (Waters, 1950). For the dye-hydrophobic fibre system, the affinity of the disperse dye decreases with increase in dyeing temperature while the saturation value of the dye in the fibre increases with increasing temperature (Bird et al, 1959; White, 1960).

Dyeing with Disperse Dyes 213

dyes must take into account the effect that effluent from the dyeing process will have on the environment, and aim to minimize such pollution. These objectives are not mutually exclusive but interrelated; they must all be taken into account in any dye development

Disperse dyes are the most important class of dye used in dyeing polyester fibres and provide a wide range of hues with good build-up and fastness properties adequate for most purposes. The rate of dyeing may be raised to the level of commercial acceptability, either by raising the working temperature to the region of 130C, or by dyeing at the boil in the presence of an accelerating agent or 'carrier' (Waters, 1950). Disperse dyes can also be transferred to polyester fibres under dry conditions by impregnating the goods with a suitable dispersion, drying and then baking at temperatures in the range 190-220C

The term 'carrier' is originated from the idea that the compound and the dye formed a complex which could 'carry' the dye into the fibre, thus causing more rapid dyeing. It is now known that the carrier is adsorbed by the fibre and operates by modifying the structure

A carrier is an organic compound, dissolved or emulsified in the dyebath. Carriers allow dyeing of even deep shades at the boil within a reasonable dyeing time. Common polyester dyeing carriers include butyl benzoate, methylnaphthalene, dichlorobenzene, diphenyl and

The actual mechanism by which a carrier accelerates dyeing has been widely debated and probably depends on the carrier used. The polyester fibres absorb the carrier and swell. This swelling can impede liquor flow in packages causing unlevelness. The overall effect seems to be a lowering of the polymer glass transition temperature, thus promoting polymer chain movements and creating free volume. This speeds up the diffusion of the dye into the fibre. A typical carrier dyeing procedure involves running the goods in the bath 60C and adding dilute dispersing agent, emulsified carrier and lastly the disperse dyes. The temperature is then gradually raised to the boil and dyeing continued at this temperature (A. D. Broadbent, 2001). The sorped carriers must be removed from the polyester after dyeing, usually by hot-air drying the goods from 150-180C. Residual carriers can adversely affect lightfastness

The benefits of carriers were overwhelming in the early days of polyester dyeing because polyester fabrics could be dyed in unpressurized becks with no more dyeing problems than with direct dyes. However, carrier dyeing has steadily declined since the development of suitable machines for dyeing polyester under pressure at temperature around 130C. Carriers are still used in some garment and small commission dyehouses where high

High temperature dyeing is the most widespread method of batch coloration. The temperatures (ca. 130C) require pressurized equipment and impart increased diffusion of

temperature pressurized dyeing machines are not available (A. D. Broadbent, 2001).

program (Leadbetter & Leaver, 1989).

(Ingamells, 1993).

**5.1 Carrier dyeing** 

if left on the goods.

**5.2 High temperature dyeing** 

**5. Main methods of disperse dyeing** 

of the amorphous regions (A. Johnson, 1989).

*o*-phyenylphenol, the latter two being the most popular.

Heat setting changes the morphology of the polyester fibres. When fabrics of polyester are heat set in air under conditions of free shrinkage, the dye exhaustion first decreases and then increase with increasing setting temperature. The minimum exhaustion occurs after seeing at around 160-190C. If applied tension prevents fabric shrinkage during heat setting, the dye uptake/temperature profile is similar to that under conditions of free shrinkage, but with higher uptake values (A. D. Broadbent, 2001).

#### **Fibre fineness**

Much attention has been given recently to dyeing microfibres. In a broad sense, especially in Europe, the term microfiber means fine fibers of less than 1.0 denier. However, in South Korea and Japan, where fine-fibre technology is more advanced, fine fibres of 0.04–0.4 denier class are generally used in this filament area (Koh et al, 2006). A useful preliminary relationship between the percentages of dye on weight of goods (C1, C2) needed to achieve a particular depth of shade on polyester fibres of two different fineness (D1, D2) was suggested by Fothergill (Fothergill, 1944):

$$\frac{C\_2}{C\_1} = \sqrt{\frac{D\_1}{D\_2}}\tag{2}$$

According to this equation, it takes much more dye to dye the microfiber to the same apparent depth as the regular fibre. Therefore, such marked denier difference can affect dyers in a number of ways (Aspland, 1997).

#### **4.3 Recent requirements in disperse dyeing technology**

Environmental issues have been gaining importance in all aspects of industrial production (McCarthy, 1998), and various legislative requirements have emerged with increasing regularity to reduce the impact of dyeing processes on the environment. In response, the industry has been forced to become increasingly innovative in order to develop new products and practices that are more environmentally friendly than existing ones (Lewis, 1999). Therefore, innovation and developments in color chemistry and dyeing will allow the colorist to meet ever-increasing environmental restrictions, produce novel effects, and reduce processing costs (Leadbetter & Leaver, 1989).

The demand for environmentally friendly dyes with high wet fastness on polyester is increasing, and the so-called alkali-clearable disperse dyes suggest a promising new direction (Fig. 8). These alkali-clearable disperse dyes obviate the need for sodium hydrosulphite and significantly reduce the cost of effluent treatment (Koh & Greaves, 2001). Recently, these types of dye have become technically important for the coloration of polyester and its cellulosic blends. They perform well on international standard and commercial wash fastness test (such as ISO C06 C2S) (Choi, 1999).

To achieve acceptable levels of wet fastness after post-heat treatment, the development of modern disperse dyes must be directed towards satisfying a number of needs. Firstly, new dyes need to be tailored towards satisfying shorter, more easily reproducible and more economical dyeing processes. Secondly, with the increasing use of polyester and polyester blends in sports and leisurewear, there is a clear demand for dyes of higher wet fastness. Indeed this requirement has become even more important with the introduction of polyester microfibres, where higher depths of shade have to be dyed in order to obtain the same visual yield as with conventional polyester fibre. Finally, the development of new disperse

Heat setting changes the morphology of the polyester fibres. When fabrics of polyester are heat set in air under conditions of free shrinkage, the dye exhaustion first decreases and then increase with increasing setting temperature. The minimum exhaustion occurs after seeing at around 160-190C. If applied tension prevents fabric shrinkage during heat setting, the dye uptake/temperature profile is similar to that under conditions of free shrinkage, but

Much attention has been given recently to dyeing microfibres. In a broad sense, especially in Europe, the term microfiber means fine fibers of less than 1.0 denier. However, in South Korea and Japan, where fine-fibre technology is more advanced, fine fibres of 0.04–0.4 denier class are generally used in this filament area (Koh et al, 2006). A useful preliminary relationship between the percentages of dye on weight of goods (C1, C2) needed to achieve a particular depth of shade on polyester fibres of two different fineness (D1, D2) was

> 2 1 1 2 *C D*

According to this equation, it takes much more dye to dye the microfiber to the same apparent depth as the regular fibre. Therefore, such marked denier difference can affect

Environmental issues have been gaining importance in all aspects of industrial production (McCarthy, 1998), and various legislative requirements have emerged with increasing regularity to reduce the impact of dyeing processes on the environment. In response, the industry has been forced to become increasingly innovative in order to develop new products and practices that are more environmentally friendly than existing ones (Lewis, 1999). Therefore, innovation and developments in color chemistry and dyeing will allow the colorist to meet ever-increasing environmental restrictions, produce novel effects, and

The demand for environmentally friendly dyes with high wet fastness on polyester is increasing, and the so-called alkali-clearable disperse dyes suggest a promising new direction (Fig. 8). These alkali-clearable disperse dyes obviate the need for sodium hydrosulphite and significantly reduce the cost of effluent treatment (Koh & Greaves, 2001). Recently, these types of dye have become technically important for the coloration of polyester and its cellulosic blends. They perform well on international standard and

To achieve acceptable levels of wet fastness after post-heat treatment, the development of modern disperse dyes must be directed towards satisfying a number of needs. Firstly, new dyes need to be tailored towards satisfying shorter, more easily reproducible and more economical dyeing processes. Secondly, with the increasing use of polyester and polyester blends in sports and leisurewear, there is a clear demand for dyes of higher wet fastness. Indeed this requirement has become even more important with the introduction of polyester microfibres, where higher depths of shade have to be dyed in order to obtain the same visual yield as with conventional polyester fibre. Finally, the development of new disperse

*C D* (2)

with higher uptake values (A. D. Broadbent, 2001).

suggested by Fothergill (Fothergill, 1944):

dyers in a number of ways (Aspland, 1997).

**4.3 Recent requirements in disperse dyeing technology** 

reduce processing costs (Leadbetter & Leaver, 1989).

commercial wash fastness test (such as ISO C06 C2S) (Choi, 1999).

**Fibre fineness** 

dyes must take into account the effect that effluent from the dyeing process will have on the environment, and aim to minimize such pollution. These objectives are not mutually exclusive but interrelated; they must all be taken into account in any dye development program (Leadbetter & Leaver, 1989).
