Permanent dyes

Melanin Drying. One development (ca 1993) in hair coloring involves the formation of pigments within the hair that are very similar to natural melanin. Thus either catalytic or air oxidation of 5,6-dihydroxyindole [3131-52-0] can be effectively used to permanently dye hair within a short time (38). The formed color can, if required, be further modulated with dilute H2O2 or can be even totally removed from hair by this oxidant. 

Hair dyeing includes the use of permanent, semipermanent, and temporary dyes. A permanent dye lasts through any number of washings as well as permanent waving. A semipermanent dye is removed after two to ten washings, and a temporary dye is largely eliminated after one washing. 

Hair dyes are of two types permanent and semipermanent. Permanent dyeing is achieved with a synthetic dye, applied with hydrogen peroxide that first bleaches the natural pigment melanin. Semipermanent dyes are generally made with vegetable extracts, such as henna, that coat rather than penetrate the hair shaft. There are a number of questions about the safety of synthetic hair dyes, since some of the products they contain cause cancer. 

Semi-permanent dyes are smaller molecules and these can pass through the outer layer of the hair, known as the cuticle, and move into the inner cortex, there to remain until they gradually leach out again and are washed away. A combination of dyes is generally required to produce the desired shade and those commonly used are listed in the Glossary. 

Colorants for other purposes, such as hair dyes, are not so strictly regulated. The ones used in semi-permanent dyes are 2-nitro-i,4-diaminobenzene, (orange/red), 2-amino-4-nitrophenol (yellow), 1,4-diaminoanthraquinone (violet), and 1,4,5,8-tetra-aminoanthaquinone (blue), and a combination of these will produce the desired shade. 

Assuming a concentration of 10% and application of 100 mL once per month for permanent dyes, and 35 mL once per week for semi-permanent dyes. Estimated that 1% of the amount apphed may be absorbed. 

USE For dyeing hair and nails auburn to red, in the Orient together with " rang, the dried, powdered Leaves of the indigo plant, in order to produce darker and even bluish-black shades. For relatively permanent dyeing the pH must be about 5.5 this is achieved by the addition of citric, boric, or adipic acid. Ingredient of many commercial hair rinses. 

For permanent hair dyes where small shade changes to a lighter color are required, bleaching is also involved. For these systems of permanent dyes, extra peroxide is formulated into the creme developer for the necessary bleaching action. For formulas of this type, see the section of Chapter 6 that describes the formulation of permanent hair dyes. 

Permanent dyes are actually formed inside the hair. Small molecules are forced into the hair and then oxidized, normally by hydrogen peroxide, into colored complexes that are too large to migrate out of the hair. The color then becomes permement on the portion of the hair that was treated. To maintain the color, you have to repeat the process as new hair grows out. This maintenance program keeps hairdressers in business. 

ATI technology can permanently dye, print, or imprint on either one side or both sides of the fabric in one continuous passage, and has no minimum order quantity. As the whole operation can be confined into about 8000 ft space, it is called an IMF, as shown in Figure 2.10. In addition to its small physical footprint, its environmental footprint is very small. This is because the fabric coloring and printing technology does not... 

Permanent dyes. Procedure is comparable with semi-permanent dyes, but the colouring is longer lasting and resistant to shampooing (Fig. 2). 

Semi-permanent dyes are usually applied to natural, unbleached hair after shampooing. The formulations use mixtures of dyes, blended to the desired shade. It is common to use several dyes of similar colour but with different molecular sizes to provide even coloration. Larger dye molecules tend to be retained by the more damaged tip of the hair, but do not penetrate so readily into the roots, while smaller molecules penetrate the entire hair fibre but wash out of the more porous tip. 

While it seems likely that the permanent oxidative process in an optimised form and the current range of semi-permanent dyes will... 

The ROK Ministry of Health and Welfare (MOHW) has published a positive list of active ingredients authorized in oxidation dyes, semi-permanent dyes and bleaching products (MOHW Decree 1995/68). It is fairly similar to the Japanese list for oxidation dyes, but 19 hair dyes and 3 bleaching active ingredients have been added by modification of the Decree on 23 August 2004. 

Semi-permanent dyes (see further on) are sometimes used at concentrations weak enough to avoid excessive duration and overintense shades. 

Nitro dyes This group of sani-permanent dyes are aromatic amines (to be exact, derivatives of p-phenylendiamine and o-phenylendiamine), aminophenols and aminophenyl ethers, which contain nitro gronps. Some examples are shown in Figure 4.3.1. 

Acid dyes They contain acid groups like -SO3H or -COOH in their molecular structure. Examples of these semi-permanent dyes are azo acid dyes (e.g. Acid Orange 7) and anthraquinone acid dyes (e.g. Acid Violet 43). Figure 4.3.2 shows the chemical structure of two of these acid dyes. 

Sometimes, semi-permanent dyes are added to the oxidation dyes to provide highlight. They do not participate either in the oxidation itself or in the oxidative condensations. 

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