Colorants processing

The first one-step print process was introduced by Land in 1947 (3). A comprehensive account of one-step photography detailing the development of instant black-and-white and color processes from 1944 through 1976 is available (4). Subsequent developments in instant photography and related reprographic processes through 1988 have also been described (5). A review of the chemistry of a number of instant color processes may be found in Reference 6. 

Fkrb prozess, m. dyeing process, dyeing coloring process. 

Plastics can be used to make erasable printing media by a number of different techniques. Photo changing dyes could be incorporated into the structure of the plastics. The printer could change the dye to the colored form to read, and the material can be bleached with another unit that would reverse the photo coloring process. An ionic type plastic can be incorporated into the plastics and used to color the printed area by the use of an indicator type reaction with an organic acid or base. Another method would be to use a thermal printer in conjunction with liquid crystal type materials that would alter the state of the liquid crystals in the printed areas. Applying heat and electrical fields to the printed sheet would erase the printing. 

IV. Color Processes and Color Matching STOtems In terms of color, we can have one of two processes ... 

The initial objective of this series of books has been to establish a coherent body of explanatory information on the principles and application technology of relevance for students preparing to take the Associateship examinations of the Society. This particular book has been directed specifically to the subject areas covered by Section A of Paper B the organic chemistry and application of dyes and pigments and of the auxiliaries used with them in textile coloration processes. However, many qualified chemists and colourists interested in the properties of colorants and their auxiliaries have found the First Edition useful as a work of reference. For several reasons it has been convenient to divide the material into two separate volumes 1. Colorants, 2. Auxiliaries. Although fluorescent brighteners share some features in common with colorants, they have been treated as auxiliary products in this book. 

Some auxiliaries fulfil more than one of the above functions. For example, an auxiliary to improve dye solubility may also accelerate (or retard) a coloration process, or an emulsifying agent may also act as a thickening agent pH-control agents may both stabilise a system and also affect the rate of dye sorption. 

A surfactant was defined in Chapter 8 as an agent, soluble or dispersible in a liquid, which reduces the surface tension of the liquid [1]. It is helpful to visualise surfactant molecules as being composed of opposing solubility tendencies. Thus, those effective in aqueous media typically contain an oil-soluble hydrocarbon-based chain (the hydrophobe) and a smaller water-solubilising moiety which may or may not confer ionic character (the hydrophile). The limitations of space do not permit a comprehensive detailed treatment of the chemistry of surfactants. The emphasis is therefore on a broad-brush discussion of the principal types of surfactant encountered in textile preparation and coloration processes. Comprehensive accounts of the chemistry and properties of surfactants are available [2-13]. A useful and lucid account of the chemistry and technology of surfactant manufacturing processes is given by Davidsohn and Milwidsky [ 14] ... 

Until recently this class accounted for by far the largest number of surfactants used in preparation and coloration processes. This dominance is now challenged by the much increased use of nonionic types. The essential feature of the class is a long-chain... 

The great majority of coloration processes demand some control over the treatment pH, which varies from strongly alkaline in the case of vat, sulphur or reactive dyes, to strongly acidic for levelling acid dyes. The concept of pH is a familiar one its theoretical derivation can be found in all standard physical chemistry textbooks and has been particularly well explained in relation to coloration processes [6,7] both in theory and in practice. We are concerned here essentially with the chemistry of the products used to control pH and their mode of action. It has been stated [7] that Unfortunately, pH control appears simple and easy to carry out. Add acid and the pH decreases add base (alkali) and the pH increases. However, pH is the most difficult control feature in any industry . 

The control of pH in textile coloration processes is ensured by three fundamentally different techniques ... 

The most common buffering system containing a weak base together with its salt formed with a strong acid is ammonia with ammonium sulphate. Some useful buffers are obtained from combinations of unrelated acids or bases with salts. The following combinations find occasional use in textile coloration processes, but the acetates and orthophosphates are most frequently used ... 

The potential of crown ethers for use as auxiliaries in textile coloration processes does not appear to have been evaluated recently, although their potential to complex with alkaline-... 

Individual size polymers may be used alone or in combination with one another and their performance may be further improved by the addition of other components such as waxes and lubricants. However, whilst sizing offers many benefits in the subsequent weaving of the yarns, it is anathema as far as wet processing is concerned. A typical sized yarn may contain as much as 34% of impurities, distributed as shown in Figure 10.15. These impurities can interfere with wetting-out and with bleaching. They may also affect coloration processes. Depending on the type of size and the dyes used, dye uptake may be increased or resisted ... 

These classes of chemicals contain not only some of the oldest dyes, dating back to the 19th centnry, bnt also some of the most important flnorescent chromophores. The earliest of these discoveries was flnorescein (3.21), which was later brominated to give the polybromo derivative eosin (3.22) (Fignre 3.10). They are of little importance in textile coloration processes bnt are nsed in some fluorescent pigments and extensively in analysis and biological methods and also in tracing the course of water in drains and other water outlets. 

These data, and the lack of concentration dependence in rigid glasses, suggest that the solute species involved in the photo-coloration process is monomolecular and has an internal 0—H N bridge. In fact, such an arrangement appears to be a prerequisite for the process. 

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