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How are the dyes we are familiar with made?

How are the dyes we are familiar with made?

  • June 3,2020.

How are the dyes we are familiar with made?



Development of dye processing technology


There are many kinds of dyes, but they can be divided into solid, liquid and slurry according to the physical form of the commodities. It can be further divided into:

* Solid dyes -- powder, granular, dust-free powdery, blocky, flaky, short columnar;

* Liquid dyes -- water-soluble liquid, dispersion;

* Slurry dyes -- solid/liquid mixture.


Dyes are organic compounds, which often complete chemical reactions in the presence of liquids, therefore, the world's first synthetic dyes were first sold in liquid form. Of course, the quality of the dyes at the first beginning is far from the present, can only be regarded as the original form of today's liquid dye. At that time, about 20% of the commodities were in liquid form, and these liquid dyes were mainly VAT dyes and mordant dyes.

By 1923, the British first added the selected additives to the original dyes and crushed them to make an dispersion of insoluble disperse dye solution. By 1910, most dyes are dehydrated and processed into a fine powder of certain specifications.


However, the initial powdery dyes had the disadvantages of serious dust flying and poor wetting properties.


Now the performance of liquid dyes has been significantly improved after the optimization of the processing formula. The storage time can reach more than half a year without deterioration. The liquid dyes with low processing costs, easy to use and get constant development.


Since 1950, the emergence of bead mill has promoted the development of post-processing technology. Wet grinding with bead mill can produce particles finer with narrower distribution. And the processing formula was improved to make the basic particles of the dye reach about 1 micron. The quality of the products produced by the new technology and equipment was significantly improved, great progress has been made in the processing of insoluble dyes.


With the progress of chemical machinery and equipment, granular dyes began to appear. The apparent granularity size of granular dyes is 100 ~ 300μm, have hollow particles also have solid particles. Its liquidity, wettability, dispersion are better than powder dyes, and also overcomes the drawback of flying powder dust. This dosage form was immediately welcomed by the production and application departments as soon as it appeared, now many dyes were processed into granular commodities.


Dye processing


The research content of dye processing technology mainly includes the determination and treatment of raw dyes, the study of the properties of processing aids, the design and selection of processing equipment and the study of processing technology.


The post-processing technology is complex, mainly because its regularity is not strong, more individuality, less generality, it is difficult to sum up quantitative law. So people say that dye processing technology is the combination of science, technology and experience.


1 - Dye processing has the following characteristics

① Many varieties to deal with. Since dyes are fine chemical products, the general production tonnage is not large, more varieties, and there are certain differences in processing methods, so the process and equipment are quite complex;

② Dyes factory needs to adjust dosage form or replace variety according to market situation, which request the processing equipment should have certain adaptability, production device is multifunctional, and has strong mobility;

③ High technical content, Post-processing includes many aspects, also involves multiple professional knowledge, during the processing there are both physical and chemical changes, many factors are interrelated and restrictive;

④ High quality requirements for products. Commercial dyes have a number of economic and technical indicators, some have been developed national standards, harsh production conditions, require stable operation, operators should have a higher quality and a stronger sense of responsibility.


2 - Dye processing content

2.1 Analysis of raw dyes

The analysis of raw dyes here refers to the testing and analysis of the physical and chemical properties of the raw dyes for the purpose of dye processing. After years of research, it is found that post-processing is not a simple physical process. Before processing the dye, it is necessary to first analyze many indicators such as the strength, color, hydrophilicity, crystal shape, energy level and impurity content of the raw dye, so as to provide basic data for determining a reasonable processing process.


After dye synthesis, the raw dye filter cake was provided to the post-processing workshop through liquid-solid separation, after receiving the filter cake, the post-processing workshop will take the raw dyes to tested.


Different dye varieties, different synthetic processes, and even different manufacturers of same variety, or different production batches from same manufacturer, all may have some differences in product quality. Each batch of dyes should be tested comprehensively, only in this way can we work out a set of correct processing methods.


2.2 Dye processing aids

Dye processing aids is the material added into the dyes during the post-processing, which can help to improve performance of specific dye commodity dosage forms (such as dispersion, thermal stability, dust resistance, prevent agglomeration, solubilization, etc.), or to improve the given performance (such as level dyeing, accelerating and darkening, etc.), and the performance of the dye on the fiber (e.g., color fixing, softness, etc.), enhance the thermal stability, maintain or improve dispersion stability, prevent dye aggregation, improve the levelness of dyeing.


In recent years, the additives used in dye processing have developed to hundreds of kinds, with the largest dosage, and the dispersant varieties that play an important role in the processing results are increasing year by year, and the physical and chemical indexes and economic indexes are also different. For example, lignin dispersant can produce many series of varieties with different molecular weights and different sulfonation degrees, you can be choose the most suitable varieties according to the needs.


For the processing of insoluble (disperse, reductive) dyes, a large number of additives need to be added in order to adjust the strength and other properties. There are many kinds of additives, which show different properties in different dyes. It is one of the research contents of post-processing technology to study the compatibility of additives to make them play the best role in the formulation.


2.3 Processing equipment

Processing equipment (post-processing equipment) is an important means to complete post-processing operations, reasonable design and selection of processing equipment is the primary condition for successful completion of post-processing operations. It can be said that the development of post-processing technology is inseparable from the progress of equipment.


In other words, the development of equipment is also promoting the continuous development of post-processing technology. In dye processing, the use of ultrafiltration and reverse osmosis membrane plays an important role in desalting of water soluble dyes and improving purity. The developement and application of PUHLER ultramicro pulverizing equipment can keep dyes particle size down to about 1 micron.


In some literatures, the processing equipment is often devided into the category of chemical equipment and regarded as the general equipment of chemical equipment. From the professional point of view of dyes, it should be regard as special equipment.PUHLER ultramicro pulverizing equipment


2.4 Processing technology

Processing technology is the method to apply the above three parts synthetically. It has been proved by practice that the same raw dyes, additives and equipment can produce completely different results by different processing techniques, indicating the importance of the process conditions. These four factors are interrelated and restrictive, and none of them is indispensable.


If the post-processing technology is reasonable, the production cost can be reduced, the production environment can be protected and the product quality can be improved.

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