When selecting additives to help improve the quality of dyed products, the following issues must be noted.
　　
　　1. Technical personnel must master the basic knowledge of additives.
　　
　　This is the prerequisite for selecting the right additives. To use additives effectively, one must have a basic understanding of the fundamental concepts, basic structure, performance, and usage characteristics of the additives. If any abnormal situations arise, one should be able to analyze the reasons and address them promptly. Therefore, I have written an overview section at the beginning of each chapter in my manual, describing the principles of action, basic characteristics, structural classification, usage methods, application testing methods, and precautions for using this type of additive, enabling readers to grasp the knowledge of these additives and lay a solid foundation for correct usage. In the subsequent introductions of each additive, I will introduce their basic structure, properties (factory standards), Applications, and usage methods. If the structural types are the same, their usage methods and performance are generally similar, allowing for extrapolation. For varieties not collected in the manual, as long as one understands their basic structure, they can be well understood. Therefore, when using new additives, manufacturers must ask suppliers to inform them of the structural categories of the additives, for example, which category the applied softener belongs to among amino silicone softeners, hydroxy silicone softeners, fatty amide softeners, imidazoline softeners, and fatty acid paraffin softeners. The applying factory should know this. Only then can they grasp the basic performance and prevent blind usage.
　　
　　2. There must be a basic understanding of the solubility of additives and their stability against hard water and metal ions.
　　
　　For example, the solubility of anionic surfactants in alkaline conditions is greater than in acidic conditions, while the opposite is true for cationic surfactants. Amphoteric surfactants have characteristics of both anionic and cationic surfactants, while non-ionic surfactants are less affected. The solubility of the first three types of surfactants increases with temperature, while the solubility of non-ionic surfactants decreases with increasing temperature, leading to the appearance of a cloud point. The cloud point must be higher than the usage temperature; otherwise, its efficiency will be lost, and the additive will not function. The cloud point increases with the number of EO units and with the amount of anionic additives added, but decreases with the increase in electrolyte content. If a common additive is used in high-temperature and high-pressure dyeing processes, the usage temperature greatly exceeds its cloud point (generally around 75°C), which will lead to precipitation in the dye bath, rendering it ineffective and causing dye aggregation, resulting in color spots. Organic silicone defoamers are emulsions made from methyl silicone oil or ethyl silicone oil with non-ionic surfactants and white carbon black. If an emulsifier with a low cloud point is used, the same issues will arise, and additive manufacturers often overlook this problem, which poses a significant risk to dyeing factories. The method for determining the cloud point is found in my manual 5-013, and the method for determining surfactant solubility is found in 6-035.
　　
　　3. The acid and alkali resistance of additives must be tested.
　　
　　This helps to understand whether the additives can meet the process requirements. The acid and alkali resistance of additives varies greatly. Anionic surfactants generally resist alkali but not acid, with phosphate esters having the best alkali resistance and carboxylic acids having the worst acid resistance. Cationic surfactants generally resist acid but not alkali. Non-ionic surfactants can resist weak acids and weak alkalis but cannot resist strong acids and strong alkalis. Dyeing factories must first test whether the additives used will cause turbidity or precipitation during use according to process requirements. One factory used imported additives for underwater belt bleaching and initially did not notice any problems, but then wrinkles appeared continuously, and irregular color spots were found on the dyed fabric. Upon opening the box, it was found that solid substances of varying thickness were stuck to the guide roller, which turned out to be precipitates from the additives that were not alkali-resistant, adhering to the fabric and forming color spots during dyeing. Therefore, the alkali and acid resistance of the additives must be tested. This is especially important during cold-rolled bleaching. Many additives will hydrolyze in alkaline and acidic media, and the testing methods can be found in manuals 6-017 and 6-018.
　　
　　4. The ionic nature of additives must be understood.
　　
　　Additives can be anionic, cationic, non-ionic, or amphoteric, with the first three being commonly used. Anionic surfactants cannot be used in the same bath as cationic additives, as they will form flocculent precipitates together, which not only will not function but will also create dye defects. Amphoteric surfactants can be used in the same bath as cationic or anionic additives. These principles are well known, but in actual production, they are often unconsciously overlooked. For example, fixing agents are cationic and cannot come into contact with anionic additives. However, many factories use anionic soap washing agents for washing after dyeing with direct, acidic, or reactive dyes, and then do not rinse the washing agent off before applying the fixing agent. At this point, the fixing agent will bond with the washing agent on the fabric, wasting the fixing agent and reducing its fixing effect, while the precipitate formed by the soap washing agent and fixing agent will affect the washing and rubbing fastness of the dyed material.
　　
　　5. Do not arbitrarily reduce the amount of additives.
　　
　　The components of dyeing additives can be roughly divided into two categories: functional additives and surfactant blends. The former uses different compounds to perform functional roles during processing, such as oxygen bleaching stabilizers, fixing agents, color repair agents, defoamers, softeners, green agents, water-repellent and oil-repellent finishing agents, flame retardants, wrinkle-resistant finishing agents, etc. They can only achieve the desired effect at a certain dosage. The other category is surfactants used as dyeing additives, such as penetrants, cleaning agents, leveling agents, refining agents, foaming agents, dispersants, emulsifiers, etc. Their effects are essentially the manifestation of the wetting, emulsifying, dispersing, and solubilizing actions of surfactants, which is a comprehensive effect or a specific performance of their functions. Therefore, it is essential to learn about surfactants. Surfactants will form micelles in solution, and the concentration at which micelles appear is called the critical micelle concentration, abbreviated as c.m.c. When the concentration exceeds c.m.c, the number of micelles increases, and the micelles grow larger. The wetting action of surfactants can occur below c.m.c concentration, while emulsifying, solubilizing, dispersing, and cleaning actions are all effective only when the concentration is above c.m.c. Generally, the c.m.c value of pure surfactants does not exceed 0.2g/L, while most commercial products contain only 15-20% active surfactant content, with a total solid content of about 40% when combined with other auxiliary materials. Therefore, the c.m.c of the resulting product is likely to be no more than 1g/L. In other words, the concentration of additives must exceed 0.5g/L to start producing micelles, and only above this concentration will the micelle quantity increase and the effect become significant. Therefore, the amount of additives cannot be arbitrarily reduced, especially for commercially available low-cost cleaning agents, which may contain only 5% active ingredients, with a large portion being fillers. If used in small amounts, the cleaning effect will not be achieved. The national standard and ISO standard stipulate a soap washing fastness test with a soap agent dosage of 3g/L for this reason. Wetting and penetration are not due to micelles but rather due to individual surfactant molecules, so they can occur below c.m.c, and the concentration in the processing solution does not need to exceed 1g/L.
　　
　　6. Add the additives to the processing liquid only after they have been dissolved and diluted.
　　
　　Due to the different specific gravities and solubilities of the raw materials in compound additives, the commercially available additive liquids often form layers with different compositions, which can affect the effectiveness. After long storage or in cold weather, turbidity or even stratification may occur due to changes in solubility. As long as it is not an emulsion, this phenomenon is still permissible. However, before weighing the materials for use, it is essential to require the operator to stir thoroughly and then weigh the materials. If it is an emulsion, turbidity and stratification are not allowed. This indicates that the emulsion has broken and cannot be used, or it must be re-emulsified through rapid stirring. It can only be used if it has been proven usable through high-speed centrifugation tests, and it must never be used just by manual stirring.
　　
　　Solid additives must be completely dissolved in hot water before use, while liquid additives must be diluted with warm water before use. Additives with very high viscosity must be gradually diluted by slowly adding water while stirring. Additives that are prone to mold, such as fatty softeners and pastes, can still be used if they have not thinned out and there are not many mold spots; the upper layer can be skimmed off, and the additive below can still be used. If it has thinned out, it should be returned.
　　
　　When adding the dissolved and diluted additives to the treatment bath, it should be based on the process requirements. Generally, they are added to the treatment liquid before the fabric enters the treatment bath. After the solution circulates to ensure uniformity, it is then introduced to the fabric. If it is a leveling agent, the fabric should be run in the leveling agent for a few minutes before adding the dye solution.