The familiar dyes, how they are made

　　Dye finishing technology progress history

　　There are many varieties of dyes, but in terms of the physical form of their goods, they can be classified as solid, liquid and slurry. They can be further divided into

　　Solid dyestuffs - powders, granules, dust-free powders, lumps, flakes, short columns.

　　Liquid dyes - water-soluble liquids, dispersions.

　　Paste dyes - solid/liquid mixtures.

　　Dyes are organic compounds, which often complete their chemical reactions in the presence of liquid, so the world's synthetic dyes were first sold in liquid form. At that time, about 20% of the goods were in liquid form, and these liquid dyes were mainly reduction dyes and mordant dyes.

　　By 1923, the British were the first to add selected auxiliaries to the original dyes and crushed them to make dispersions of insoluble disperse dyes in aqueous solution. By 1910, most of the dyestuffs were finished to a fine powder of definite specifications after the water was removed.

　　According to the literature in 1924, about 80% of the dyestuffs were then finishing into fine powder form, and reduction dyestuffs had been made into powdered dye goods with a wide particle size distribution, from very fine to 50 um. However, the initial powder dyes had the disadvantages of severe dust flying and poor wetting performance.

　　After 1930, further progress was made in the dispersion form of dyes, but the disadvantages of easy precipitation of dyes and poor storage stability still existed.

　　Nowadays, liquid dyestuff has improved significantly after optimizing the finishing formula, and the storage time can reach more than half a year without deterioration, and liquid dyestuff has been progressing with low finishing cost and ease of use.

　　Since 1950, the advent of sand mills has promoted the progress of post-treatment technology, adopting sand mills for wet grinding to obtain particles with finer particle size and narrower distribution. The finishing formulations were improved so that the basic particles of dyestuff reached about 1um, and the quality of products produced by the new technology and equipment was significantly improved, and the finishing of non-water-soluble dyestuff made greater progress.

　　With the progress of chemical machinery and equipment, granular dyes began to appear. Granular dyes have an apparent particle size of 100~300um, with hollow and solid particles. Their fluidity, wettability and dispersibility are better than those of powdered dyes, while overcoming the shortcomings of dusty powdered dyes, and this dosage form was immediately welcomed by the production and application sectors as soon as it appeared.

　　Dye Finishing

　　The research of dye finishing technology mainly contains the determination and treatment of the original dye, the study of the performance of finishing additives, the design and selection of finishing equipment and the study of the finishing process.

　　If the finishing technology is complex, it is mainly because it is not very regular, with more individuality and less commonality, and it is difficult to summarize the quantitative laws. So people say that the dye finishing technology is a combination of science, technology and experience.

　　A. Dye finishing has the following characteristics

　　① processing of many varieties, because the dyestuff is a fine chemical product, the general production tonnage is not large, many varieties, finishing methods have certain differences, so the process and equipment is quite complex.

　　② dyestuffs need to adjust the dosage form or change varieties according to market conditions, requiring finishing equipment should have a certain adaptability, multi-functional production equipment, a strong mobility.

　　③ high technical content, finishing after treatment contains a variety of content, also involves a number of professional knowledge, in the finishing process there are both physical and chemical changes, many factors are interrelated and mutual constraints.

　　④High product quality requirements, commodity dyestuffs have a number of economic and technical indicators, some of which have been developed national standards, harsh production conditions, requiring stable operation, operators should have a high level of literacy and a strong sense of responsibility.

　　II. Dye finishing involves several aspects

　　2.1 Analysis of the original dyestuff

　　The analysis of the original dyestuff here refers to the testing and analysis of the physical and chemical properties of the original dyestuff for the purpose of dye finishing. After years of research, it is found that post-treatment is never a simple physical process. Before finishing the dyestuff, the strength, color integrity, hydrophilicity, crystallinity, energy level, impurity content and many other indicators of the original dyestuff should be analyzed to provide basic data for determining a reasonable finishing process.

　　After the synthesis of dyestuff, the liquid-solid provides the original dyestuff filter cake for the post-treatment workshop respectively, and the post-treatment workshop first tests the original dyestuff after receiving the filter cake.

　　Different dyestuff varieties, different synthesis process, even the same variety of different manufacturers, the same manufacturer of different production batches, product quality may have some differences, each batch of dyestuff should be measured in all aspects, only then can we develop a set of correct finishing method.

　　2.2 Finishing auxiliaries

　　The so-called dyestuff finishing auxiliaries is in the process of finishing dyestuff, added to help improve the performance of specific dyestuff commodity formulations (such as dispersion, thermal stability, dust resistance, anti-coalescence, solubility, etc.) or conducive to improving the given performance (such as leveling, promote dyeing, deepening, etc.) and dyeing performance on the fiber (such as color fixation, softness, etc.) substances, enhance heat resistance, maintain or improve the stability of the dispersion, prevent dye coalescence, and Substances that help to improve the uniformity of coloring.

　　Commercial finishing is inseparable from auxiliaries, and without knowledge of the properties of finishing auxiliaries, it is impossible to optimize the finishing formula. The correct use of auxiliaries can improve the quality of dyes, reduce production costs and increase the added value of dyes.

　　In recent years, the auxiliaries used in dye finishing has progressed to hundreds of species, a large amount, and the finishing results play an important role in the dispersant varieties are increasing year by year, the physical and chemical indicators and economic indicators vary. Such as lignin dispersant, has been able to produce different molecular weight, different sulfonation degree of a number of series of varieties, you can choose the appropriate species according to the needs.

　　For non-water-soluble (dispersion, reduction) dyes finishing, the need to add a large number of additives to adjust the strength and other aspects of performance, many varieties of additives, used in different dyes show different properties, the performance of additives as well as physical and chemical indicators to determine the scope of his use. Only to understand the performance of the correct use, the study of the compatibility of additives to play a good role in the formulation of additives is one of the post-processing technology research.

　　2.3 Finishing equipment

　　Finishing equipment (post-treatment equipment) is an important means to complete the post-treatment operations, reasonable design, selection of finishing equipment is the primary condition for the successful completion of post-treatment operations. It can be said that the progress of post-processing technology cannot be separated from the progress of equipment.

　　In other words, the progress of equipment is also promoting the continuous progress of post-treatment technology. In dye finishing, the use of ultrafiltration and reverse osmosis membranes plays an important role in the desalination of water-soluble dyes and improves purity. The development and application of ultra-micro crushing equipment can reduce the particle size of dyes to about 1μm. The application of drying technology and equipment is also very extensive. At present, there are many professional manufacturing plants of drying equipment for the development and research of dye drying equipment, which has formed a unique station of the industrial sector, and the domestic drying equipment can basically meet the needs of dye drying.

　　Some literature tends to divide the finishing equipment into the category of chemical equipment, and regard it as the general equipment of chemical equipment. From the dyestuff professional view should also be regarded as special equipment. In the dye finishing post-processing due to the characteristics of dye production and commercialization, the connection between these factors is particularly close, general-purpose equipment used without special effects, commodity quality to some extent has a strong dependence on the equipment, only targeted design to play a large potential of the equipment.

　　2.4 Finishing process

　　The finishing process is a comprehensive application of the above three components. Practice has shown that the same original dyestuff, additives and equipment, the adoption of different finishing process to get very different results, which shows the importance of the process conditions. From the above introduction, it is easy to see that these four aspects mark the level of technology of post-treatment.

　　Many large foreign companies have their own professionals engaged in this area of research, and some are even engaged in the post-treatment technology development personnel more than synthetic personnel. If the post-treatment finishing process is reasonable, it can achieve the purpose of reducing production costs, caring for the production environment and improving product quality.

　　These four factors are both interrelated and mutually constrained, one cannot be without the other. It can be considered that the comprehensive application of the above four factors, is the specific embodiment of the level of post-processing technology.