Basic knowledge about vat dyes

Vat dye definition

Vat dyes are insoluble in water and cannot be used to dye fabrics directly. When dyeing, it is necessary to use insurance powder in an alkaline solution to reduce the leuco body to a water-soluble leuco body, so that it can be adsorbed by the fiber, and then oxidized and developed by air, etc., to convert the leuco body into the original dye and dye it on the fiber.

According to the structure, the dyes can generally be divided into two categories: the anthraquinone family and the indigo family. The former such as Vat Blue RSN, Vat Brown BR, Vat Gray, etc.; the latter such as Vat Blue 2B, Vat Pink, etc. Vat dyes generally have more complex molecular structures. However, they are often composed of some simple basic structures. Anthraquinone is the basic structure of the anthraquinone family; the basic structures of the indigo family are indigo and thioindigo. Moreover, they all contain carbonyl group C=O. This group has hydrogenation and reduction properties, and the reaction that occurs during the dyeing process is carried out on this group. After the successful development of reactive dyes, although some of them were replaced by this dye, they are still very important dyes for printing and dyeing cellulose fiber textiles. Vat dyes can also be used for vinylon dyeing. There are some vat dyes that can be used to dye polyester fibers as disperse dyes.

Characteristics of vat dyes

1) Most colors are middle colors

The colors of vat dyes are characterized by a complete range from yellow to black, from bright colors to ordinary colors. It is characterized by the majority of intermediate colors. These intermediate colors are basically a single component and have good dyeing reproducibility, especially green, olive green, flesh color, brown and gray series.

2) Excellent light fastness and various light fastness composites

Currently, the requirements for various composite fastnesses of cotton fabrics based on light fastness are getting higher and higher, especially for light colors. Compared with other types of cotton dyes, vat dyes have great advantages, so they are very suitable for dyeing and printing work clothes, summer clothes, sportswear, coats, curtains, furniture coverings, etc.

3) Excellent chlorine resistance fastness

Compared with reactive dyes, vat dyes also have excellent chlorine resistance, so vat dyes are suitable for occasions with high requirements for chlorine disinfection and washing resistance. In addition, vat dyes are also very suitable for dyeing and printing textiles that require the highest level of wet fastness, such as ground dyeing with reactive dyes and textiles with anti-pull-out printing with vat dyes.

4) Excellent stability for fabric finishing processing

Vat dyes have minimal discoloration of general resin finishing. In recent years, vat dyes have good stability in functional processing that changes the physical properties of fibers, such as shape memory processing, deodorant processing, antibacterial processing, etc. In addition, vat dye dyeing has more stable change over time than reactive dye dyeing.

5) Suitable for one-bath same-color dyeing of blended fabrics

One-bath same-color dyeing of polyester/cotton, nylon/cotton, vinylon/cotton and other blended fabrics is increasingly popular in the printing and dyeing industry. Vat dyes have the characteristics of isochromatic dyeing and are suitable for one-bath continuous dyeing, printing and exhaust dyeing of these blended fabrics. These dyed fabrics can be used to make student uniforms, uniforms, breathable coats and special textiles, especially military uniforms and combat uniforms (such as camouflage uniforms), and have various excellent dye fastness and infrared resistance properties.

6) Excellent reduction resistance

This characteristic of vat dyes can be used to produce high-end textiles with reactive dye ground dyeing and vat dye pull-out printing, floor-less dyeing of polyester-cotton knitted fabrics (liquid flow dyeing machine), and pre-dyeing processes for polyester-cotton blended fabrics (cheese yarn). Dyeing) and high-fastness printing and dyeing of polyester/cotton blended fabrics (using URS method, that is, ultra-high-speed steaming method), etc.

7) Has a natural tone

Fabrics dyed with vat dyes can express natural plant tones and European-style features based on coarse tones. For example, by subjecting indigo ground dyeing and vat dye direct printing dyeing fabrics to various washing treatments (stone washing, bleaching, etc.), textiles with extremely clear and natural plant tones can be made. In summary, compared with other cotton dyes, vat dyes have a series of significant characteristics, especially reflected in the dye fastness performance. Therefore, vat dyes are still a type of cotton dyes worthy of attention.

Vat dye applications

1. Dip dye

Vat dye-dyed cotton fabrics mainly use the dip-dying process, and cheese dyeing machines or beam dyeing machines can be used depending on the processing volume. In recent years, in order to adapt to the high quality of cotton knitted fabrics, liquid flow dyeing machines are also used. In addition, in response to the requirements of small batches and rapid processing, garment dyeing will increase.

2. Continuous dyeing

The vat dye suspension pad-steaming process is used for continuous dyeing, which is suitable for large-volume fabric processing such as work clothes, coats and bedding; while jig dyeing is suitable for small batches; it is especially suitable for wide-width fabrics and can be used for thick fabrics such as tents. efficiency.

3. Printing

The most common method of vat dye printing is one-phase printing using potassium carbonate and anti-migration agent. A high-end printed textile that is very popular in Europe, the United States and Japan is printed cotton fabric that is ground-dyed with reactive dyes and discharge-dyed with vat dyes. in addition. The UPS method used for mass processing uses two-phase printing, which is most suitable for direct printing of outer covers, sleeves, etc.