Based on the differences in dyeing characteristics and types of different reactive dyes and the composition and properties of alkali substitutes And performance, compare the chemical properties and characteristics of traditional soda ash and trisodium phosphate, alkali substituters, soda ash, trisodium phosphate and other alkali agents, various analysis on the fixation of reactive dyes, and introduce in detail the effects of various alkali agents on reactive dyes functions and application advantages.
Alkalis commonly used in printing and dyeing
In reactive dye dyeing, fixation The traditional alkali agents used in the reaction are relatively mild soda ash, trisodium phosphate, and some alkali substitutes.
As a special alkali agent for fixing reactive dyes, it is used to replace traditional alkali agents such as soda ash. However, in the specific application of alkali substitutes, due to their different chemical composition, properties, and performance from traditional alkali agents, they have their own characteristics, and thus have different applications.
Chemical properties and characteristics of traditional alkali agents
Reactive dye dyeing The fixation reaction needs to be carried out under certain alkaline conditions. The selection of alkali agents has traditionally been based on soda ash and trisodium phosphate. Strong alkali such as caustic soda is rarely used alone.
1. The alkalinity of soda ash is relatively mild, and its chemical properties are suitable for reactive dye dyeing. The pH value of its aqueous solution does not change much within a relatively wide unit concentration range. ; Trisodium phosphate also has this property, but it is more alkaline than soda ash.
2. The changing characteristics of the pH value of soda ash in aqueous solution are related to its chemical properties. After soda ash is dissolved in water, it reacts reversibly with water to generate sodium hydroxide and sodium bicarbonate. Under humid and hot conditions, sodium bicarbonate will gradually release carbon dioxide to generate soda ash and water, thereby increasing the pH value of the solution. It maintains a fairly constant state; when it meets caustic soda, it generates soda ash and water, so it has an anti-alkali effect in some situations, so sodium bicarbonate is also called acid sodium carbonate. Therefore, within a certain unit concentration range, the pH value of the solution does not change much, which is very suitable for dyeing with reactive dyes and can make the fixation reaction process between dyes and fibers proceed smoothly and continuously.
3. The chemical characteristics of trisodium phosphate are the changes in its pH value in aqueous solutions with different unit concentrations. Although the impact and mechanism of action are not the same as those of soda ash The same, but it has the same effect as soda ash. Although its alkalinity is stronger than soda ash, it is weaker than caustic soda, and it is within the range suitable for reactive dye dyeing, so it is often used in dye fixation reactions, especially for reactive dyes that require relatively high pH values. Sometimes it is also mixed with soda ash according to specific varieties.
4. Caustic soda and other strong alkalis are very alkaline, so small changes in unit concentration will also cause significant changes in pH value, and due to the lack of soda ash and trisodium phosphate With such buffering performance, although the dosage when reaching the specified pH value is very small, except for a few dye varieties, it is difficult to achieve better coordination and controllability in the dyeing reaction with most reactive dye varieties. Therefore, in actual large-scale production It is mainly mixed with trisodium phosphate in an appropriate proportion and is used in some varieties of thermosetting dyes. It is basically not used alone. If the pH value of the dye bath is too high (most varieties cannot be higher than 12), the proportion of dye hydrolysis will rise linearly.
Dyeing characteristics and type differences of reactive dyes
Usually, the reaction Soda ash is used for the more reactive dichlorotriazine-type reactive dyes, while stronger alkali agents, such as trisodium phosphate, or a mixture of trisodium phosphate and caustic soda can be used for the less reactive monochlorotriazine-type reactive dyes. Alkali agent, of course, it is not impossible to use soda ash, but the dosage needs to be increased. At this time, you need to pay attention to the problem of alkali bloom when dyeing dark colors. If caustic soda is involved, the temperature can be appropriately lowered.
When the pH value of the dichlorotriazine reactive dye bath is less than 9.0, the fixation rate is very low. After it exceeds 9.0, the fixation rate begins to rise sharply, and when the pH value reaches 10.0~ The maximum value often appears at 10.5.
For monochlorotriazine reactive dyes, the fixation rate begins to increase significantly when the pH value reaches 10.0, and the maximum value occurs when the pH value is 11.0 to 11.5.
The activity level of vinyl sulfone reactive dyes is between dichlorotriazine type and monochlorotriazine type. The alkali concentration of the fixing bath can generally be equal to that of dichlorotriazine type. The type is similar, but the temperature should be higher than it, lower than monochlorotriazine, and somewhere in between. There are also some varieties where it is advisable to increase the fixing reaction temperature to the conditions of monochlorotriazine type dyes in order to increase the color quantity.
B type, M type and other isomeric dual reactive group type reactive dyes, different brands, different origins and different varieties, the isomerization ratio may be different. They are different, but it is necessary to consider and take into account the characteristics of both monochloros-triazine and vinyl sulfone, and it is not advisable to be too biased towards one side. The fixing bath temperature can also be slightly higher than that of the vinyl sulfone type.
Because the reaction process of reactive dyes fixing on cellulose fibers must first be carried out under certain alkaline conditions, but it will gradually release acid and chlorine during the reaction process. The active chlorine atoms in triazine, in the presence of alkali agents and under certain conditions, are prone to covalent bonding reactions with the hydroxyl groups (primary alcohol groups) in the molecular structure of cotton fibers to generate cellulose ethers.Multiple reactive group types such as reactive groups have become the mainstream variety of reactive dye dyeing, accounting for the largest proportion of the entire reactive dye usage, so alkali substitutes have a wide range of applications.
2. Alkali substitutes mainly replace traditional alkali agents such as soda ash. They are aimed at the fixation reaction. There are no specific requirements for conditions such as temperature and time in the dyeing process. Alkali substitutes The principle of action also determines that although it is not directly related to the leveling problem, it should be diluted and added to the dye bath.
3. Alkali substitute replaces soda ash. After all, the two are not the same chemical substance, so the chemical reactions that occur are different, and the color light after fixation cannot be completely Same. Therefore, it is inappropriate to use the small sample made with soda ash to hold the large sample with alkali substitute. The same alkali agent must be used for the small sample and the setting out.
4. Since the total amount of alkaline agent is greatly reduced, and the difference in unit concentration usage between dark, medium and light colors is much smaller than that of soda ash Much more, so the measurement must be as highly accurate as the dye.
5. Due to the acid release phenomenon during the fixation reaction of reactive dyes, when the amount of dye increases, the amount of alkali agent should increase accordingly. However, due to the presence of dyes in the dye bath, rapid pH measurement at large production sites in workshops is susceptible to interference from the color of the dye bath, and its accuracy is difficult to guarantee.
In order to be safe, the amount of soda ash used is often increased. Therefore, after dyeing with deep and thick colors, alkali flowering is easy to occur. Although alkali flower is not a real color flower, and it is necessary to increase the amount and strength of the washing water to overcome it, when using soda ash, the washing water consumption is larger; if the cloth is not thoroughly washed with alkali, the weather fastness of the finished product will be changed. Poor, long-term storage can easily lead to bond-breaking in the dye, resulting in poor wet treatment fastness. This is especially true for dyes containing vinyl sulfone groups. </p
