This article explains the principle of acrylic fiber dyeing, the description and application of important parameters in the dyeing process, and focuses on the accumulation of practical results. Provide valuable wealth for promoting acrylic fiber dyeing technology.
Acrylic fiber dyeing mechanism
The macromolecules of polyacrylonitrile fibers are acidic, and dyeing them with cationic dyes can be regarded as an ion exchange process. The ion exchange reaction between dye ion D+ and fiber FSO3H or FCOOH can be expressed by the following formula: FSO, -H++D+=FS0-D++H+ or FC0O-H++D+=FCOO–D4-+H+ in acrylic fiber , due to the existence of acidic groups and the strong electronegativity of cyano groups, under dye bath conditions, the fiber surface is negatively charged and has a very high electrodynamic layer potential with a value of approximately (44-58mV).
Dyeing process analysis: Because the cationic dyes are combined with the acidic (cationic) groups in the fiber through salt bonds. Due to different fiber production processes. There are also differences in the number of acidic groups in the fiber. Dyes that are not bound to the acidic groups in the fiber have poor wet fastness. Therefore, the dye saturation value of cationic dyes should not exceed the dye saturation value of ionically bonded fibers.
Compatibility (compatibility)
When different cationic dyes are mixed together for dyeing. They may have different dye uptake rates (competition dyeing) when dyed individually, so the compatibility of dyes is a very important performance. Compatibility refers to the fact that when two or more dyes are combined, the dyeing rate is equal, and as the dyeing time is extended, the color (hue) always remains unchanged (only the shade changes) British Dyers Association.
1. The compatibility value is small. High affinity, fast dyeing speed, poor level dyeing, high color yield, good for dyeing dense or medium-dark colors; (color matching: the difference in compatibility values is not greater than 0.5).
2． Dyeing acrylic fiber with cationic dyes mainly involves localized adsorption. Its adsorption isotherm belongs to the Langmuir type and has a saturation value.
3. Dyeing saturation value: The percentage of the maximum weight of dye that can be dyed on the fiber when dyeing reaches equilibrium.
Adsorption isotherm and dyeing saturation value
Dye saturation value SD: refers to the dyeing saturation value of commercial cationic dyes on a certain type of acrylic fiber under specified conditions. The saturation value of the dye is a constant for a certain cationic dye-acrylic system.
Dye saturation coefficient (relative saturation value): the quotient obtained by dividing the saturation value of the fiber by the saturation value of the dye. It refers to the relative relationship between the saturation values of different dyes and standard dyes on the same fiber.
The saturation coefficient is a constant for a certain cationic dye, which determines the ability of the dye to dye acrylic fiber: small f means high dyeing amount and strong color; the saturation value of the fiber and the saturation value of the dye are the measures of acrylic dyeing. Performance and important parameters for formulating a reasonable dyeing process; acrylic fibers with low saturation values are difficult to dye into dark colors; when dyeing, the amount of dye used cannot exceed the saturation value of the dye on the fiber: when color matching, the sum of the dyes used does not exceed The fiber saturation value should be exceeded.
Level dyeing
The dye has a high affinity for acrylic fiber. The initial dyeing rate is high and the acrylic fiber has a tight structure. The dye has poor diffusivity and migration: TTg, the dyeing rate is rapid. Measures:
1. Slow down the dyeing speed; final dyeing High temperature and long dyeing time are conducive to leveling dyeing
2. The dyeing concentration has a great relationship with the dye leveling property. When the dyeing concentration is low, uneven dyeing is more likely to occur;
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3. When the dyeing concentration is low, the dye uptake rate is fast. The time required to complete dyeing is short, so uneven dyeing in the initial dyeing has a greater impact on the levelness of the product.
4. When the dyeing concentration is low, local uneven concentration in the dye bath can easily cause uneven dyeing;
5. Dyeing When the concentration is low, concentration changes cause the dyeing rate to change greatly, and slightly different dye concentrations will cause uneven dyeing
6. When the dyeing concentration is high. Changes in concentration have little effect on changes in dyeing rate. Differences in dye concentration may not necessarily cause obvious color differences
7. The closer the dyeing is to saturation, the easier it is to obtain level dyeing. Dyeing path temperature control (key).
Dyeing operation method
Slow heating method: after reaching the glassy state Above the conversion temperature, slowly increase the temperature. Generally, the method of raising the temperature by 1°C every 2 to 4 minutes is used.
Sectional heating method: between each heating section. It can be kept for a period of time, and then raised to 100oC for dyeing, which is conducive to leveling dyeing; keep it at 85-90℃ for 10-15min; keep it at 95℃ or 97℃ for 20-30min: the dyeing rate will increase a lot after insulation, and the holding time will definitely increase; after insulation The dye uptake rate did not increase. Keeping warm can be canceled or another keeping warm temperature can be found.
Constant temperature dyeing method: Always dye at a constant temperature of 85-95℃ for 45-90rain, wait until most of the dye is absorbed, and then raise the temperature to 100℃ for dyeing.
Other precautions
1. Optimum temperature 97~105 ℃, the duration at high temperature is 45-90min. For light colors, the temperature can be lower and the time can be shorter; for dark colors, the temperature can be increased and the dyeing time can be extended; the temperature is too high. It feels hard and the fabric is deformed. It is not advisable to drop the temperature suddenly after dyeing, otherwise it will affect the feel.
2. The pH value controls the number of ionized sulfonic acid groups or carboxylic acid groups, which not only affects the fiberThe dyeing saturation value of �� also affects the dye uptake rate.
The pH value of the dye bath decreases, which can reduce the dissociation of acidic groups in the fiber, resulting in lower dye adsorption capacity and lower dyeing rate. The influence of pH value on the dyeing saturation value and dyeing rate is more significant for acrylic fibers containing carboxyl groups; usually the amount of acid used when dyeing light colors is higher than when dyeing dark colors, so that the pH value is lower to obtain better level dyeing. In order to increase the dye uptake percentage when dyeing dark colors, the amount of acid should be less.
Acid is essentially a dye retardant. When dyeing, the pH value of the dye bath should be well controlled. Generally, the pH value of the dye bath is between 4 and 4.5. This will not only make it easier to obtain better uniformity. Dyeability and high dyeing percentage. At the same time,
ionic dyes have good stability and high solubility in weakly acidic media. Because the pH value is too high (under alkaline conditions), the dye will change color and even precipitate. When dyeing dark colors, if the pH value of the dye bath is too low, there will be fewer ionized acidic groups in the fiber, which will cause a reduction in the dye uptake percentage.
3. Application of retarder: There are two types of retarder: cationic retarder and anionic retarder. The dosage should be appropriate. If it is too much, it will prolong the dyeing time and affect the dyeing fastness; if it is too little, it will not have the effect of retarding dyeing. Most quaternary ammonium salts with long-chain hydrocarbon groups are colorless compounds with positive charges, which can be ionized in solution to generate retarder cations.
For example, dodecyldimethylbenzyl ammonium chloride (i.e. retarder HG-2401). Retarder cations compete with dye cations to reduce the dyeing rate of cations. The size of the competitive dyeing effect depends on the nature and amount of retarder and dye. Cationic retarder also has a saturation value and saturation coefficient, and its dosage should not exceed the saturation value of the fiber. The retarding ability of cationic retarder is related to the size of its molecular structure and its affinity to fibers. Therefore, some retarders (such as retarder HG-2401, etc.) are mainly based on retarding, while other retarders are based on retarding. Promote the migration of cationic dyes to achieve level dyeing.
Dye migration effect: Helps the dye to move from the parts with high dyeing amount to the parts with small dyeing amount. The general dosage is 1.5% to 5.0%. Do not overdose.
Diffusion, penetration and cleaning effect: Local deep spots with floating color are prone to occur. Adding leveling agent HG-2101 can solve the problem of deep spots.
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