Cold pad batch dyeing is a semi-continuous dyeing method that realizes the dyeing of cotton knitted fabrics through processes such as semi-product pre-treatment, pad dyeing solution, rolling, stacking, washing, soaping, washing and drying. Environmentally friendly dyeing.
1 Pre-treatment preparation
The cold pad-batch dyeing process uses low-temperature dyeing. Penetrating into the fiber, the impurities, slurry, spinning oil and machine oil stains on the fabric to be dyed must be completely removed during treatment, and the treated fabric must have uniform and good wettability.
In addition, the remaining chemical agents such as hydrogen peroxide and alkali on the cloth surface must be washed away before dyeing, otherwise it may easily cause low color yield or uneven dyeing. The drying process must also be well controlled to ensure uniform moisture regain. Excessive drying will lead to poor fabric wettability and poor reproducibility when enlarging samples. Therefore, a humidity control system should be used during drying.
2 Selection of dyes for dyeing process
The selection of dyes should be based on directness, reactivity and color fixation rate. comprehensive consideration.
The dye has low directivity, which can reduce head-to-tail color difference, but too low directivity will affect the adsorption and color fixation of reactive dyes during dyeing, so choose direct dyes containing vinyl sulfone groups and s-triazine multi-reactive groups. A dye with medium resistance is more suitable.
Dye reactivity is low, and the fixation rate is very low at room temperature. However, the highly reactive dichloro-s-triazine (X type) reactive dyes have poor diffusivity on fibers and are affected by pH value. The influence is greater, floating color is prone to occur, wet fastness is poor, and color difference is not easy to control.
During mixed dyeing, the dyeing speed of each component dye should be balanced to reduce the head-to-tail color difference, color difference between batches, etc. In addition, considering the problems of grooving, roll changing, etc. in large-scale production, In order to maintain the consistency of color light during temporary parking and other situations, there are also certain requirements for the alkali hydrolysis stability of the dye. The dye needs to have the characteristics of medium directness, good diffusivity, good permeability, good alkali resistance, excellent washability, stable color and light, good reproducibility and high color fixation rate.
3 Preparation of dye liquor
In order to ensure that the dye can fully diffuse into the fiber before fixation and improve the color fastness, A suitable alkaline agent must be selected. Someone once used an alkali solution system composed of sodium silicate and caustic soda. Although sodium silicate can stabilize the pH value of the dye liquor, it is easy to scale on the fabric and the roller, causing stains or fabric scratches, and the fabric after dyeing is also damaged. It feels a bit stiff. In view of the above reasons, a lye system composed of soda ash and caustic soda is used to adjust the appropriate pH value for different dye dosages.
In order to improve the fixation rate and reproducibility of the dye and prevent the dye from being hydrolyzed in the alkali agent, the dye liquor and the alkali liquor should be prepared separately and then added to the mixing container through a feeding pump with automatic and precise metering control. Premix before adding to padding tank. The feeding pump can fully mix the two components, speed up the exchange of dye liquor, and ensure the uniformity and stability of the dye bath concentration in the dye tank. In order to avoid leaving the mixed dye liquor for too long, the volume of the rolling tank should not be too large, preferably around 30L.
4 Pad dyeing equipment
For the cold pad batch dyeing process of knitted fabrics, the dyeing pad car is the core of the entire device.
Since knitted fabrics are easy to curl, and when the warp tension is too high, the fabric surface is easily elongated, causing weft shrinkage, weft skew, and even a decrease in fabric surface density, so the cloth feeding system is equipped with an automatic Central unwinding device and tension adjustment device to ensure that the fabric enters the padding car evenly and smoothly. At the same time, a fan-shaped expansion device is used when feeding the fabric. On the one hand, it can center and expand the fabric, and on the other hand, it can ensure that the tension of the fabric fed to the pad car is low.
In addition, in order to ensure consistent pressure on the upper and lower sides of the fabric, some equipment companies use vertical roller arrangements for the dyeing pads used for elastic fabrics, and the clamping guide rollers are also changed from the conventional horizontal arrangement to the most advanced. Optimized 70° arrangement, that is, a group of rollers are arranged obliquely according to the cloth path. The upper and lower sides of the fabric are simultaneously fed into the rolling point at the same angle to prevent differences in rolling pressure on both sides of the fabric. The diagonally placed guide rollers reduce the tension on the fabric during the pulling process.
5 Rolling and stacking
After passing through the pad car, the fabric is sent to the rolling device through the guide roller. In order to avoid the knitted fabric being rolled during the rolling process Due to the color difference caused by tension changes, the A-frame needs to be automatically driven to wind up. That is, as the cloth volume increases, through the control of the tension detection device, the A-frame moves away from the roller at a constant speed from the initial position to achieve constant tension. , constant linear speed to ensure smooth winding of fabric after dyeing.
The rolled fabric should be sealed and wrapped tightly with plastic film to prevent the reaction heat released by the dye during the color fixation process from dissipating, otherwise it will cause color difference due to the temperature difference between the inside and outside of the roll. It can also prevent Migration caused by the drying of the outer cloth surface during long-term storage, or the pH value dropped due to carbonation of the cloth edges, slowing down the dye fixation rate and causing the cloth edge color difference. During the stacking process, start the motor to make the cloth roll rotate slowly.
6 Washing
In order to fully remove unreacted dyes and hydrolyzed dyes on the fabric, roll and stack for a certain period of time before unwinding , and washed in an open-width drum washing machine to remove floating colors to improve the wet fastness of dyed knitted fabrics. You can wash it in hot water first and then cold water. If the requirements for washing fastness are very high, you can first soap and wash, and then use a fixing agent to fix the color. </p
