Product Description
Product Properties of Acid Dyes
- Chemical Properties
Chemical Structure
Molecules contain water-soluble groups such as sulfonic acid groups (-SO3H) and carboxyl groups (-COOH), usually existing in the form of sodium or potassium salts, which endow them with good water solubility.
Chromophoric systems are mostly azo, anthraquinone, triphenylmethane types, etc. Among them, azo acid dyes account for the largest proportion. Their structures contain chromophores such as azo groups (-N=N-), which give the dyes various colors (e.g., red, yellow, blue, orange).
The molecular structure is relatively simple, with a small molecular weight (generally between 300-800), and they have strong affinity for protein fibers (e.g., wool, silk) and polyamide fibers (e.g., nylon).
Chemical Stability
They are relatively stable under acidic conditions and suitable for use in dye baths with a pH of 2-6; under strongly alkaline conditions, they may undergo hydrolysis or structural damage, leading to changes in color shade or a decrease in dyeing ability.
They have poor stability to oxidizing agents and are easily damaged by bleaching agents, resulting in fading; their stability to reducing agents varies by type, and some azo acid dyes may be reduced and decomposed.
- Physical Properties
Appearance
Most are in the form of powder, granules, or liquid, with rich colors covering various color spectra such as red, yellow, blue, green, orange, and purple. The brightness of the color varies by type (e.g., anthraquinone acid dyes have brighter shades and better light fastness).
Solubility
Due to the presence of water-soluble groups, they are easily soluble in water, forming uniform dye solutions; some acid dyes with complex structures (e.g., acid mordant dyes) have low solubility and require dispersants or heating to improve solubility.
They have a certain solubility in organic solvents such as ethanol, but it is usually not as good as in water.
Other Physical Properties
The melting point is relatively high, generally above 200°C, and most have no definite melting point and are prone to decomposition when heated;
The density is usually between 1.3-1.6 g/cm³, depending on the molecular structure.
- Dyeing Properties
Applicable Fibers
Mainly used for dyeing protein fibers (wool, silk, rabbit hair, etc.) and polyamide fibers (nylon 6, nylon 66). Because these fiber molecules contain polar groups such as amino groups (-NH2) and amide groups (-CONH-), which are protonated under acidic conditions, they can combine with anions of acid dyes (e.g., -SO3) through ionic bonds to achieve dyeing.
Some acid dyes (e.g., acid complex dyes) can also be used for coloring leather and paper.
Dyeing Conditions
Dyeing medium: It needs to be carried out under acidic conditions (e.g., adding sulfuric acid or acetic acid to adjust pH). The acidic environment can promote fiber protonation and enhance the binding force with dyes.
Dyeing temperature: Varies by dye type. Weak acid dyes are usually dyed at 70-100°C, while strong acid dyes require boiling conditions (100°C) to achieve good dye uptake.
Dyeing Methods
Common methods include dip dyeing and jigger dyeing. Sodium sulfate can be added to the dye bath as a dyeing accelerator to improve dye uptake; some types need to add leveling agents to improve levelness.
After dyeing with acid mordant dyes, they need to be treated with metal salts (e.g., chromium salts) to form stable metal complexes, so as to improve wash fastness and light fastness.
Color Fastness
Light fastness: Anthraquinone acid dyes have good light fastness (up to 4-5 grades), followed by azo types (3-4 grades), and triphenylmethane types are relatively poor (2-3 grades);
Wash fastness: Strong acid dyes have poor wash fastness (2-3 grades) due to their weak binding force with fibers, while weak acid dyes and acid complex dyes have stronger binding force, with wash fastness reaching 3-4 grades;
Perspiration fastness and rubbing fastness: Generally good, but wool needs attention to post-treatment after dyeing to avoid rubbing fading.
- Classification and Characteristics (by dyeing conditions and structure)
Acid dyes are widely used in textile, leather, printing and dyeing industries due to their bright colors and convenient application. Their performance can be further improved through molecular structure modification or dyeing process optimization.
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