Functional dyes are a type of dyes with special functionality or special expertise. This special function is usually related to the properties of light, electricity, heat, chemistry, biochemistry and other properties associated with modern high and new technology fields. This type of dye absorbs very little energy and can produce certain special functions. Therefore, it is used in small quantities and at a high price, and has significant economic benefits.
At present, functional dyes have been widely used in high-tech fields such as liquid crystal displays, thermo-sensitive pressure-sensitive recording, optical disc recording, photochemical catalysis, photochemical therapy, etc. in some countries. All major dye companies in Japan regard the production of functional dyes as the focus of their respective development. In addition to photography, electrostatic copying, copying and other varieties, domestic functional dyes have almost no applications in other fields, or are still in the trial production stage, and have not attracted enough attention. In particular, the application of functional dyes in dyeing and finishing has only just begun to take shape, and its research, manufacturing, application, and management levels are still far behind those of advanced countries. It should be said that functional dyes are a valuable tool for dye workers and dyeing and finishing workers. Strive to explore new areas.
1 Classification and Development Approach of Functional Dyes
1.1 Classification of Functional Dyes
Functional dyes are in a stage of rapid development, and their classification is not uniform. They can be classified as follows according to their functions.
Color-changing isomeric dyes: photochromic, thermochromic, electrochromic, wet-chromic, pressure-sensitive (pressure-sensitive) color-changing dyes
Energy conversion dyes: dyes for luminescence, solar energy conversion, laser, organic nonlinear optical materials, etc.
Functional dyes Dyes for information and display recording: liquid crystals, color filters, dyes for optical information recording, electronic copying, inkjet printing (printing), etc.
Biochemical and medical dyes: biological coloring, medical dyes, etc.
Chemical reactions Dyes used: catalytic, chain-terminating dyes, etc.
1.2 Development approaches for functional dyes
There are two main development approaches for functional dyes: one is to screen original dyes and utilize certain potential properties of traditional dyes and pigments . The second is to change the color system of traditional dyes to give them new functions.
2 Application of functional dyes in textile dyeing
At present, photochromic dyes, fluorescent dyes, infrared absorption and camouflage dyes, thermochromic dyes, moisture-sensitive (heat-sensitive) coatings, electrochromic dyes, special colored dyes Functional dyes such as polymers, metal ions, solvent-chromic dyes, and far-infrared thermal insulation coatings have entered the practical stage in textile dyeing and finishing or have shown their potential application prospects.
2.1 Photochromic dyes and pigments
Compounds with “photochromic (that is, the color of a substance changes with light) properties” are called “photochromic dyes (pigments)”. Currently, there are not many photochromic dyes used directly in textiles. The main reason is that the light fastness of these dyes is not ideal, they are expensive, their affinity for fibers is not high, and they are difficult to process through conventional dyeing and printing processes. However, it can be predicted that with the development of textile dyeing and finishing processing technology and photochromic dyes, photochromic textiles will gradually mature.
2.2 Fluorescent dyes and pigments
The definition of fluorescent dyes is not uniform. Generally speaking, dyes that can strongly absorb and radiate fluorescence in the visible light range are called fluorescent dyes. Fluorescent pigments are essentially resin solid solutions of very fine-particle fluorescent dyes.
Rhodamine and its derivatives are the earliest fluorescent dyes used in textiles. They can dye silk, polyester, nylon and other natural or synthetic fibers to obtain eye-catching colors and effects. Fluorescent yellow tennis balls are dyed with fluorescent yellow dye. Made of tennis ball surface fiber material.
Fluorescent pigments are mainly used for printing or coating processing on textiles, and are used for clothing or textile products that require bright colors, such as travel supplies, sportswear and children’s clothing. At present, this type of pigment has become increasingly popular.
2.3 Infrared absorbing dyes and infrared camouflage dyes
Infrared absorbing dyes refer to dyes that have strong absorption of infrared rays. Like ordinary dyes, these dyes also have specific Л-electron common orbital systems. The difference is that they The first excitation energy is relatively low, and it absorbs not visible light but infrared rays with longer wavelengths. Infrared camouflage dyes (or pigments) refer to dyes with specific colors whose infrared absorption characteristics are similar to those of the natural environment. The difference from ordinary dyes is that their infrared absorption characteristics are similar to those of the natural environment. They can camouflage dyed objects and make them difficult to detect. Discovered by infrared observation.
In recent years, near-infrared absorbing dyes closely related to textile dyeing and finishing have been used for solar energy conversion and storage. Plastic films or textile clothing processed with this dye (or pigment) have good application prospects in industry, agriculture and clothing.
Infrared camouflage dyes (or pigments) are mainly used for camouflage of military equipment and combatants. Since infrared camouflage research is highly confidential in various countries, relevant technologies are rarely published. Information obtained from relevant patent documents shows that a small number of screened vat dyes not only have good infrared absorption properties, but also have various color fastness properties. The strength can also meet the requirements of military textiles.
2.4 Thermochromic dyes and pigments
Dyes (pigments) with “thermal color change” are called thermochromic dyes (pigments). The earliest dyes used in color-changing printing of textiles were some dyes used for thermosensitive recording. In recent years, thermochromic dyes have been increasingly used in dyeing and printing of textiles.
2.5 Moisture-sensitive and heat-sensitive coatings
Moisture-sensitive and heat-sensitive coatings are inorganic coatings made of cobalt salts. These two coatings can be used according to the usual pigment printing process, but in general, the discoloration sensitivity and color depth of this type of color-changing coating are low, the washing fastness is not good enough, and they are sensitive to acids and alkali, and need further research. .
2.6 Electrochromic dyes
When the direction of the instantaneous dipole moment of the dye is changed by an electric field, a type of dye whose color also changes with the electric field is called an electrochromic dye, or an electrosensitive dye. If textile materials are used as the base material, this electronically controlled color-changing functional dye can be made into the desired product, such asSuch as large color displays, light-shielding materials, etc., will have some special functions and are worthy of study.
2.7 Colored polymers
Colored polymers refer to molecular polymers that have their own color system. In fact, colored polymers can be used to color the dope of plastics or fibers. In the same way, coating, pigment printing and dyeing foam printing should be able to use this kind of colored body. Polymer pigments have the advantages of pigment coloring and solvent-soluble dye coloring. They can even react with the dyed polymer and combine into one through covalent bonds, so they are worthy of further research.
2.8 Metal ion and solvent color-changing dyes
Metal ion color-changing dyes refer to a type of dye that can chelate with metal ions to cause color change. Solvent-chromic dyes refer to a type of dye that changes color depending on the polarity of the solvent. Metal ion color-changing dyes make it possible to obtain multi-color dyeing or printing products due to their color-changing properties, and have certain application prospects in the textile and clothing industries; solvent color-changing dyes can be used for coloring fabrics and clothing, making these textiles exposed to water or other The solvent produces a discoloration effect, and the development prospects are optimistic.
2.9 Far-infrared thermal insulation coating
Coatings made from inorganic ceramic powder with strong infrared emission characteristics and some magnesium aluminum silicate are called far-infrared thermal insulation coatings. Far-infrared thermal insulation coating is mainly used to process sunlight heat storage insulation fabrics. In addition, through pigment printing or coating processing, it can also give the fabric the function of emitting infrared rays, making the fabric have good heat insulation or heat preservation properties.
3 Application prospects of functional dyes in other fields in the dyeing and finishing industry
3.1 Functional dyes for electrophotography
Electrophotography is also called photoelectric imaging, including photoelectric copying and laser printing, which all involve light and electricity. The interaction requires the use of some special dyes. This photographic technology has good prospects in textile dyeing and finishing.
3.2 Functional dyes for electrostatic, ion and magnetic imaging printing
Electrostatic, ion and magnetic imaging printing methods are three non-contact printing technologies, although they are not as good as electrophotography, inkjet printing and thermal printing technology popular, but they all have their own characteristics.
Electrostatic imaging can be used in the dyeing and finishing industry, as long as the surface of the textile is insulated, and electrostatic color-developing toners that have affinity for fibers and can be prepared from specific functional dyes are used for printing, and the dye is fixed on the textile through heat treatment .
Ion deposition printing technology can print original or full-color images and has high application prospects in textile printing. The key is to develop toners suitable for textiles, which means developing or screening suitable functional dyes.
The advantage of magnetic imaging printing is that it can be transferred continuously and repeatedly, and the printing speed is very high. The disadvantage is that the resolution is not high and the drum is easy to corrode, so it is suitable for printing some simple and large images. And unlike ordinary transfer printing transfer paper, which has problems such as contamination and difficulty in handling after printing, textiles will notIt must be cleaned and the process is simple; however, the price of the toner and the impact of the magnetic materials in it on the color and textile properties have yet to be solved.
3.3 Functional dyes for inkjet printing
Inkjet printing uses nozzles to eject ink (or color liquid) to form text or images on paper. Some new functional dyes can meet its requirements. With the promotion of inkjet printing technology, textiles are gradually using this principle for printing, that is, inkjet printing, which has developed rapidly in recent years.
3.4 Functional dyes for thermal diffusion transfer and thermal wax transfer
The basic principle of dye thermal diffusion technology (referred to as D2T2) imaging is very similar to transfer printing of textiles, so it is also a promising technology for the production of color printed fabrics. However, there have been no special reports on functional dyes that are particularly suitable for thermal diffusion transfer printing of textiles, and most of them are currently in the research and development stage.
It is unlikely that hot wax transfer technology will be directly used on textiles, but this transfer method is very simple. If you find a film-forming substance with strong adhesion to textiles, such as some low-melting point adhesives instead of wax, As a pigment dispersion and transfer medium, which is commonly referred to as pigment transfer technology, it is still very promising.
3.5 Functional dyes for biochemistry and medicine
Functional dyes have been used in biology and chemistry for a long time. Mainly used for cell coloring, sterilization, enzyme purification and analysis, etc. The antibacterial and antiseptic properties of dyes are of great significance to the processing of textiles with hygienic functions. Textiles dyed with such dyes can not only meet certain color requirements, but also have antibacterial and antiseptic functions. Therefore, textiles dyed with some functional dyes have medical and health care functions, and it is very meaningful to carry out research in this area.
3.6 Functional dyes for laser radiation
Lasers are currently mainly used in communications, medical care, spectroscopy, photochemistry, reaction kinetics research, isotope separation, microanalysis, military industry, and its processing applications in textile dyeing and finishing. It has also become a new trend, such as laser engraving, fiber laser modification, and functional dye printing with laser radiation.
4 Conclusion
The types and functions of functional dyes are constantly expanding with research in various fields. This article only introduces some dyes that have been or are being developed and applied. In addition to these, in fact many organic compound dyes with conductive, magnetic, catalytic and other properties belong to the category of functional dyes.
The application of functional dyes will definitely have a broader prospect, and it is closely connected with high technology and new product development. The dyeing and finishing industry is an important sector in the traditional application of dyes. In the past, the light and color properties of dyes were mainly used. In the future, although the fields of light and color will still be inseparable, in the process of developing new products, especially fiber products for industrial use, attention will be paid to the multi-faceted performance of dyes. Therefore, the application of functional dyes in the textile dyeing and finishing industry will be very potential.
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