The pretreatment agent is generally used as a base, an acid, an oxidation type-based bleaching agent, a surfactant, an enzyme preparation for desizing a starch slurry, and the like.
(a) alkali and acid
1. Alkali is commonly used as caustic soda. The main component of industrial caustic soda is sodium hydroxide, solid caustic soda (generally 95% or more) and liquid caustic soda (content 30% to 42%). Solid caustic soda is convenient for long-distance transportation, storage and storage. Liquid caustic soda is convenient to use, but the volume is convenient. Larger. Since caustic soda is produced by the salt electrolysis method, carbon dioxide in the air is also easily reacted with caustic soda to form sodium carbonate, so the soda ash content in the caustic soda should be greater than 1% to 3%, and the sodium chloride content should be greater than 1.5% to 3%. Caustic soda is a strong alkali, which is extremely corrosive to skin and mucous membranes. Pay attention to labor protection when using it. Especially when dissolving solid caustic soda, the operator must wear labor protection products. Caustic soda is an important chemical agent in cotton and cotton fabric printing and dyeing factories. It is often used in fabric desizing, scouring, mercerizing, etc. in the pretreatment process. The standard alkali consumption per 100 m of fabric is 0.8 to 1.2 kg.
Soda ash is a salt in chemical classification. It is alkaline after hydrolysis in aqueous solution. It is weak in alkali and cannot replace caustic soda. It is generally used as a softener, a scouring agent for color fabrics, and a scouring agent for protein fibers.
Ammonia is rarely used in cotton printing and dyeing plants, and is sometimes used for scouring of liquid ammonia mercerizing and acetate fabrics.
Others still have alkaloids (and hanging glass), which are auxiliaries for scouring and hydrogen peroxide bleaching.
2. Acids are commonly used in sulfuric acid. It is used for pickling, scouring and bleaching, and after mercerizing. Industrial sulfuric acid generally has a H2S04 content of 92.5% to 98%. The product is brown with a small amount of iron, sulfur dioxide and organic matter. Concentrated sulfuric acid is highly corrosive and should be handled gently when handling. When concentrated sulfuric acid is added with water, a large amount of heat energy can be generated. When diluting concentrated sulfuric acid, the acid can only be slowly poured into cold water. If it is properly stirred, water must not be injected into concentrated sulfuric acid because sulfuric acid is a poor conductor of heat and has a strong Water absorption performance, if the high heat generated by water can not be immediately released, a part of the water will boil rapidly, causing sulfuric acid to injure people with steam splash, corrosive skin and clothing. Concentrated sulfuric acid should be stored in a ventilated, dry place when stored, to avoid exposure to heat or rain, which may cause an explosion.
Hydrochloric acid acts the same as sulfuric acid and can also be used to neutralize alkaline agents. However, the price of sulfuric acid is relatively low, the acid content is high, the neutralization ability is strong, the industrial hydrochloric acid concentration is low, and the neutralization ability is as concentrated sulfuric acid, so the sulfuric acid is mainly used in the pretreatment.
(two) bleach
Both cotton and cotton fabrics are bleached with an oxidizing bleaching agent. The following oxidized bleaching agents are commonly used.
Hydrogen peroxide
Commonly known as hydrogen peroxide, it is used for bleaching cotton fabrics and polyester-cotton blended fabrics with good results. Industrial hydrogen peroxide contains 30% hydrogen peroxide and contains a small amount of sulfuric acid as a stabilizer. 30% hydrogen peroxide solution is very irritating to the skin, and it is decomposed and exploded when exposed to metal such as iron, copper, chromium, etc., exposed to heat or sunlight. Store in a cool, shady place. Long-term storage of active ingredients will be reduced, so it should be stored for a long time.
Hypochlorite
It is formed by reacting chlorine with a base. The product reacted with lime is called bleaching powder (which is a bismuth salt of calcium hypochlorite and calcium chloride, which is generally represented by CaOC12). The excellent bleaching powder contains about 30% to 35% of available chlorine. A general-purpose bleaching powder containing high effective chlorine compared to ordinary bleaching powder (effective chlorine refers to the active ingredient of bleaching powder, that is, the amount of chlorine gas generated after a certain amount of bleaching powder reacts with acid, expressed as a percentage).
Since the bleaching powder is a calcium salt, it is convenient to use, and almost all of the sodium hypochlorite is currently used except for the small plant. Sodium hypochlorite is the product of the reaction of chlorine with caustic soda and is a mixture of sodium hypochlorite and sodium chloride. Sodium hypochlorite can be made by the printing and dyeing factory, or it can be used in chemical plants.
Commercially available sodium hypochlorite is a colorless or light yellow liquid containing 100-140 mg/L of available chlorine. The performance and use of sodium hypochlorite is the same as that of bleaching powder, and is generally used for bleaching low-grade cotton fabrics and cotton blended fabrics.
3. Sodium chlorite is used for the bleaching of high-grade fabrics, and the effect is better than hypochlorite, and the whiteness is stable. Due to the high price of sodium chlorite, the requirements for corrosion resistance of equipment are high, and the decomposition product C1O2 of sodium chlorite is highly toxic, and it is currently used in China.
(3) Surfactants
Printing and dyeing processing is almost always carried out in an aqueous solution. Due to the large surface tension of water, the aqueous solution cannot wet and penetrate the fiber quickly and well, which is not conducive to the printing and dyeing process. To this end, a substance that reduces the surface tension of water is often added to water, which is called a surfactant. Usually only a small amount of surfactant is added to the water to significantly reduce the surface tension of the water. There are many such substances, such as common soap, red oil, flat plus 0. Surfactants can be mainly classified into wetting penetrants, emulsifiers, dispersants, detergents, etc. according to their performance. Although surfactants have a variety of properties and uses, they share a common feature of their molecular structure, namely, both hydrophilic and hydrophobic groups.
Hydrophilic group refers to an atomic group having a greater affinity with water. Hydrophilic groups commonly used in surfactant molecules are carboxyl groups (-COONa), sulfonic acid groups (*SO3Na), sulfate groups (*0-SO3Na), ether bonds. (*0*) and so on. The hydrophobic group is also called a lipophilic group, and is an atomic group having a large affinity with oil, such as a hydrocarbon group (C17H35-, C12H25-).
A commonly used surfactant classification method is divided into two types according to the charge of the surfactant after being dissolved in water, and the ionic surfactant can be further classified into a cationic type. There are three types of anionic and amphoteric types, as follows:
Surfactant can significantly reduce the surface tension of water. The degree of reduction is within a certain concentration range, which is related to the concentration of surfactant. When the concentration reaches a certain value, the surface tension of the solution is no longer reduced. The minimum concentration required to achieve a minimum surface tension of the solution is called the critical micelle concentration (CMC). Different surfactants have different critical micelle concentrations, and the concentration of surfactant used should be greater than the critical micelle concentration in order to fully function.
In general dyeing and finishing, two types of surfactants, anionic and nonionic, are mainly used. Commonly used are the following varieties:
(1) Anionic surfactants:
Pull open powder: It is a good wetting agent.
Red oil: usually made of castor oil and sulfuric acid, has good wetting properties, and is often used in fabric scouring.
Soap: It is a high-grade fatty acid sodium salt with excellent performance. However, it is easy to form a precipitate of fatty acid calcium and magnesium salt in hard water, and it is easy to separate the fatty acid in an acidic solution, thereby losing the washing ability and making the cloth body hard. It is difficult to remove if it sticks to the guide roller of the device.
Sodium Alkylbenzene Sulfonate (ABS): It is the main component of household detergents. It is resistant to acid and hard water and has good detergency.
The diffusing agent NN0: is mostly used as a dispersing agent for dyes during dyeing.
(2) Nonionic surfactants:
Penetrant JFC (and hanger EA): acid and alkali resistant, stable to hard water, used in desizing additives, pickling, bleaching, etc.
Pingping plus 0: has a strong diffusion ability, are used for dyeing and printing.
Anionic surfactants cannot be used in the same bath as cationic surfactants, otherwise they will combine with each other to fail each other. For other cationic additives and dyes as well, the same bath will also cause dyeing. Conversely, cationic surfactants are generally not used in the same bath as anionic builders or dyes. However, the ionic surfactant and the nonionic surfactant can be used in the same bath. At present, surfactants develop rapidly and have a wide variety of them. In the printing and dyeing process, the best surfactants should be selected to improve the quality of printing and dyeing products.
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