Denim is a warp-dyed denim fabric, which is usually woven into denim by warp dyeing. Indigo dye is usually used for dyeing denim yarn. Since indigo dye is insoluble in water and has no affinity for water, indigo dye has poor dyeing performance on cellulose textile raw materials. Therefore, indigo dye cannot be directly dyed on cellulose textile raw materials. Indigo must be reduced to a soluble leuco salt in a strong alkaline solution with a strong reducing agent. The carbonyl group in the dye molecule forms a hydrogen bond with the hydroxyl group in cellulose and fixes on the fiber yarn. The indigo leuco salt on the cellulose fiber is oxidized to indigo by air, thereby achieving the purpose of indigo dyeing. Due to the low affinity of indigo dye with cotton fiber, repeated dipping and oxidation are required in the traditional indigo dyeing process to achieve the ideal color.
Foam technology has been maturely applied to the finishing direction of textiles, but in the dyeing direction of textiles, there is still a problem that the dye liquid is difficult to penetrate into the yarn, resulting in floating color and low color fastness on the surface of the dyed yarn.
Introducing an indigo foam dyeing method for improving the dyeing fastness of denim yarn, comprising the following steps:
Cationic modification of the yarn to be dyed
The denim yarn to be dyed is unwound from the warp beam at a uniform speed, and the denim yarn is passed through a soaking tank containing a cationic modifier solution, sodium bicarbonate is added to the cationic modifier solution in batches, and the solution in the soaking tank is slowly heated to a temperature of 60-70°C after stirring evenly. The speed of the denim yarn during soaking is 20-35m/min, and a roller is provided at one end of the soaking tank. The excess soaking solution on the surface of the impregnated denim yarn is removed by the roller, and the residual rate is 80-90%;
The cationic modifier is a cationic polyacrylamide modifier
The concentration of the cationic modifier solution is 3-8% (owf)
Sodium bicarbonate is added to the solution three times, and the concentration of sodium bicarbonate is 20-25g/L.
Plasma treatment of yarn to be dyed
The denim yarn after the roller enters the low-temperature plasma equipment for treatment. Nitrogen is used as the discharge gas in the low-temperature plasma equipment, and the discharge pressure is set to 2200-2500Pa. The plasma treatment discharge power is 50-80W, and the denim yarn speed is 20-35m/min. The plasma treatment of the denim yarn surface is completed in the cavity of the low-temperature plasma equipment;
Preparation of indigo dye foaming liquid
In 80-300g/L pre-reduced indigo dye, a foaming agent, a stabilizer, a thickener and a fixing agent are added in sequence to prepare an indigo dye foaming liquid;
The foaming agent is an anionic surfactant foaming agent. The indigo dye foaming liquid is stirred in an oxygen-free environment to form an indigo foam, and the foam density is 0.02-0.05g/cm3;
The foaming agent is a compound of sodium dodecyl sulfate and a silane coupling agent in a mass ratio of 2:1-3:1, and the mass of the foaming agent is 3-5% of the indigo dye foaming liquid.
The stabilizer is dodecanol, and the content of dodecanol is 1.5-2g/L.
The thickener is sodium carboxymethyl cellulose, and the concentration of the thickener is 2-2.5g/L.
The color fixer is prepared by mixing silica sol and sodium silicate in equal proportions, and the concentration of the color fixer is 3-5g/L.
The foaming time of the indigo dye foaming liquid to form indigo foam is 5-6min, and the foaming speed is 1000-1200r/min.
The foaming agent is prepared by compounding anionic surfactant sodium dodecyl sulfate and silane coupling agent. Sodium dodecyl sulfate and silane coupling agent can increase the viscosity of the liquid film of the formed foam, slow down the drainage speed inside the foam, and slow down the drainage speed close to the liquid film, which can increase the stability of the foam and form a highly stable water-based foam. The addition of silane coupling agent can make the indigo dye foam and denim yarn more adherent, thereby improving the dyeing efficiency.
Foam dyeing
In an oxygen-free environment, indigo foam is evenly applied to the denim yarn for continuous foam dyeing. The sizing speed is 20-35m/min. After the foam is dyed on the denim yarn, the foam is squeezed by the sizing roller to break the foam, so that the sizing liquid is evenly attached to the surface of the denim yarn. The denim yarn enters the delayed oxidation box filled with inert gas for delayed oxidation;
The foaming ratio of the foam is controlled to be 1:5-1:12, so that the foam size is appropriate and the foam dye can be evenly coated on the yarn.
Dyeing is completed
The treated denim yarn is oxidized, washed, and dried to complete indigo dyeing and sizing. The dyed and sized denim yarn is wound onto the weaving shaft under constant tension.
Results and advantages summary:
The denim yarn to be dyed is first impregnated with a cationic modifier solution to graft cationic groups onto the fiber surface. Plasma treatment of the denim yarn not only improves the wettability of the fiber surface, but also promotes the reaction between the cationic agent and the fiber surface, and improves the reactivity and grafting rate of the fiber surface. The treated yarn is dyed with an indigo dyeing foaming solution added with anionic surfactants. The indigo dye foam can better penetrate into the yarn. The yarn treated with the cationic modifier is then indigo dyed. The dyeing K/S value is increased from 11.3 to 22.09, the color fastness reaches 4-5, the dry rubbing color fastness reaches 4-5, the wet rubbing color fastness is 3, and the sunlight color fastness reaches 4. All the color fastness values are at a good level.