Dyeing process pressure

An important innovative technique to replace water as the solvent in dyeing processes is the use of supercritical fluids, for example, supercritical CO2 for dyeing processes. Successful trials have been conducted in various scales with different fibers and full-scale production has been performed in the case of PES dyeing [62,63]. Besides the handling of high pressure equipment, the development of special dyestuff formulations is required. 

Typically the chromophores used are pH sensitive, i.e. acidochromic or ionochromic (see section 1.4), and the medium is one whose pH varies with temperature. A variety of pH sensitive chromophores are known that are readily synthesised and can be modified to provide a wide range of shades. Application of these pH sensitive dyes in pressure and thermally sensitive papers for digital printing, e.g. fax papers, where the whole object is for the process to be irreversible, will be covered under ionochromism. The main area of application for reversible indirect thermochromic materials is as thermochromic organic pigments, as will be described below (section 1.3.4.1). 

Another classification is based on covering up material differences in textured PES fibers. Dyes that have a low fastness to thermo fixing often hardly mark differences in texture they dye at relatively low temperature and are suited to carrier dyeing processes. Dyes that are very fast to thermofixing diffuse slowly into the fiber and must be dyed at high temperature they are not suited for carrier dyeing under atmospheric pressure they tend to mark texture and fixing differences in the fiber. 

Dyebath/auxil iary bath reuse has been demonstrated on a pilot-scale to be a feasible, economical alternative to conventional batch dyeing processes. Atmospheric disperse dyeing of nylon and polyester carpet and nylon pantyhose, and pressure disperse dyeing of polyester yarn packages have all been demonstrated as suitable candidates for plant incorporation of the reuse techniques. 

Excellent nonsilicone defoamer for high temperature pressure dyeing processes. Effectively controls foam throughout the entire polyester dyeing cycle. 

Defoamer for atmospheric and pressure dyeing processes. Effective in printing systems. 

It has been stated (J.S.D.C., 1968, 84, 66) that the productivity of one man looking after a group of five high pressure dyeing machines was increased by 37 per cent by the introduction of automatic process control. The reason is that there are a number of occasions when more than one operation should be carried out simultaneously and this cannot be done manually. Another factor is the human inability to move and react mentally with instantaneous speed. Many more examples could be quoted to demonstrate the advantage of the elimination of human memory and manual manipulation in the operation of dyeing processes. 

Supercritical fluid refers to the phase of a substance with both temperature and pressure higher than the critical point (the point where liquid and gaseous phases of a substance become indistinguishable). This phase of a substance enjoys many advantages and can replace water in the dyeing process. The supercritical fluid normally used is carbon dioxide (CO ), as the critical temperature and pressure are easier to achieve than that of other substances. 

To quantify the effectiveness of atmospheric pressure plasma on textile dyeing, dyne bath coloration is evaluated to obtain exhaustion curves which identify the kinetic behavior of dyes during dyeing processes as a function of process operating parameters. There are a number of such documenting curves for plasma treatments to wool, for example as presented by the research of Holme [21]. 

Uses Leveling agent for pressure dyeing of polyester offers min. oil emulsification props, allowing one-bath scour/dye processing Features Contains no carrier act. soivs. requires no foam control agent Properties Amber thick liq. readily disp. in wann water (> 2 C) dens. 8.4 Ib/gal pH essentially neutral... 

High Pressure in the Chemical Industry. The use of high pressure in industry may be traced to early efforts to Hquefy the so-called permanent gases using a combination of pressure and low temperature. At about the same time the chemical industry was becoming involved in high pressure processes. The discovery of mauveine in 1856 led to the development of the synthetic dye industry which was well estabUshed, particularly in Germany, by the end of the century. Some of the intermediate compounds required for the production of dyes were produced, in autoclaves, at pressures of 5-8 MPa (725-1160 psi). 

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