Uses of Acid Dyes

Acid dyes are water-soluble anionic dyes that contain acidic groups such as sulfonic acid (-SO₃H) or carboxyl (-COOH) in their molecular structure. They are mainly used for dyeing in acidic to neutral dye baths. Their main uses are concentrated in the following aspects:

Textile fiber dyeing: This is the most important application area of acid dyes.

Wool:

Acid dyes are one of the preferred dyes for wool dyeing. They can provide very bright, full, and excellent fastness (especially wet fastness) colors. They are widely used in dyeing wool yarn, wool tops, wool fabrics (such as worsted and woolen), wool sweaters, carpets, etc.

Silk:

The main component of silk is also protein (fibroin), so acid dyes are also important dyes for silk dyeing. It can give silk bright, translucent, and soft colors, and is widely used in dyeing silk fabrics, scarves, ties, etc.

Nylon (nylon):

Nylon is a polyamide fiber, and its molecular end contains amino groups (-NH₂), so it can also be dyed with acid dyes. Acid dyes dye nylon with bright colors, relatively simple dyeing methods, and low costs. They are widely used in dyeing nylon products such as socks, sportswear, swimsuits, underwear, carpets, fishing nets, ropes, etc. However, the dyeing properties and fastness of different types of nylon vary.

Leather dyeing:

Acid dyes are often used for dyeing leather, especially leather products that need to be dyed thoroughly and brightly colored. They can penetrate the leather fibers well, giving the leather rich and full colors, and are often used for upper leather, clothing leather, luggage leather, etc.

Paper dyeing:

In the papermaking industry, acid dyes can be used to produce colored paper, such as decorative paper, gift wrapping paper, handmade paper, filter paper, etc., providing bright tones.

Ink manufacturing:

Some acid dyes can be used to make inks, such as inkjet printer inks, marker pen inks, etc., providing water-soluble bright colors.

Special fields:

Food coloring (limited): It is extremely important to note that not all acid dyes can be used in food! Only specific types of acid dyes (often called food colorings) that have undergone rigorous toxicological evaluation and have been approved as food additives by relevant agencies (such as FDA, EFSA, China's National Health Commission, etc.) can be used for coloring food, beverages, drug coatings, and cosmetics (such as lipstick). Common food colorings such as lemon yellow, sunset yellow, carmine, allura red, and brilliant blue belong to the category of acid dyes in terms of chemical structure, but their purity and safety requirements are much higher than those of industrial dyes.

Biological staining:

In biological and medical research, certain acid dyes can be used to stain cells or tissue sections under a microscope to observe specific structures. For example, eosin is a typical acid dye, which is often used in combination with hematoxylin (basic dye) (H&E staining).

Aluminum anodizing staining: Some acid dyes can be used to stain the surface of aluminum products after anodizing.