The cold roll batch process is a processing process at room temperature. Because the cold roll batch processing technology has low investment cost, low energy and water consumption, high flexibility and productivity, It has many advantages such as strong process adaptability and low fabric strength loss. It is currently widely used in pre-treatment, dyeing, printing and finishing in cotton fabric dyeing and finishing processing.
The pre-treatment process of the cold pad mainly includes desizing, scouring and bleaching. The steam stacking is changed to room temperature stacking, which greatly saves energy and equipment investment. , and is suitable for small batch and multi-variety processing requirements.
Cold pad batch dyeing has a short process flow, simple equipment, and little environmental pollution. It saves energy because it does not require drying and steaming. It has a small liquor ratio and a high color yield. It has the characteristics of high color fixation rate (15-25% higher than the conventional pad steaming method) and no dye migration problems. It is especially suitable for production of multiple varieties and small batches such as tension-sensitive and opaque dyeing. In recent years, with the increase in energy costs in my country, the improvement of dye quality, and the introduction of new varieties, it has become more and more common for printing and dyeing factories to adopt cold pad batch dyeing technology.
1 Characteristics of cold pad-batch dyeing
Cold pad-batch dyeing has a short process flow and simple equipment. It has little environmental pollution. It saves energy because it does not require drying and steaming. It has a small liquor ratio, a high dyeing rate (the fixation rate is 15-25% higher than the conventional pad steaming method), and there is no dye migration problem. Features, especially suitable for production of multiple varieties and small batches such as those that are sensitive to tension and cannot be dyed through.
2 Actual large-scale production process
1. Add alkali according to The method of dyeing is divided into two processes
One is to pre-mix the dye and alkali agent to form a dye solution for padding the fabric; the other is to separate the dye and alkali agent Preparation, when padding, the metering pump is added to a small-capacity mixer at the same time in proportion.
The former process is suitable for dyes with weak reactivity, using weakly alkaline alkali agents, and the storage time is long, while the latter process is suitable for dyes with strong reactivity. For dyes, use a strong alkaline agent and have a shorter storage time.
2. Cold pad batch dyeing process
Pre-treatment semi- Product→Dyeing→Padding (dyeing with concentrated alkali agent)→Rolling and wrapping paper→Rotating and stacking→Washing→Soaping→Washing→Drying.
2.1 Preparation before cold reactor
2.1.1 Dyeing materials Choice
The dye liquor mainly consists of dyes and alkali. The working fluid is composed of dye and alkali agent, and then mixed through a 4:1 ratio pump before rolling the groove. Pad dyeing solutions generally use uniform rolls. The volume of the roll tank is preferably less than 50 liters. The vehicle speed should be faster to complete the circulation of the bath solution as soon as possible. This process has a wide range of dye options, including single/double vinyl sulfone type, monochloro-s-triazine/vinyl sulfone type, and monofluoro-s-triazine/vinyl sulfone type reactive dyes.
The specific principles are that the dye must have strong reactivity and can complete color fixation at high temperatures; the solubility of the dye in alkali must be high, otherwise the dye will aggregate and produce color spots; The stabilization time of the dye solution should be long; the tolerance of the fixation and storage time should be large to meet the needs of various production schedules; cleaning should be easy; and the color matching compatibility should be good.
Considering that large-scale production involves slotting, roll changing, temporary parking, etc., to maintain the consistency of color and light, the choice of dye stability against alkali hydrolysis is the most important. The alkali agent is a mixture of sodium silicate and caustic soda. Caustic soda provides enough alkalinity for dye reaction and color fixation, and sodium silicate alkali agent serves as a buffer to adjust the pH value of the alkali solution, thereby controlling the hydrolysis reaction of the dye, which is beneficial to improving the color fixation rate and color yield. It can avoid the color difference between front and back.
In addition, sodium silicate can also be used as an adsorbent. It is hydrolyzed into colloidal silicic acid or alkaline earth silicate in the post-treatment water bath, which can adsorb hydrolyzed reactive dyes in the water. Prevents staining on fabrics. After the fabric is dyed and rolled, it is wrapped in plastic film. The rotation and stacking time shall be greater than the maximum color fixing time in color matching. Due to production needs, it is okay to extend the storage time to 48 hours. However, if the storage time is too long or the wrapping is not tight, or the amount of alkali is insufficient, drying migration will occur, or the edges of the fabric will carbonate, resulting in a decrease in pH value and slowing down the dyeing process. Fixed color, causing color difference on the edges of the fabric.
After cold stacking, the dye fixation rate can reach 90%. Water washing is relatively simple and can be completed on any washing equipment. Generally, it is cold water washing → hot water washing → soaping (conventional detergent) → hot water washing → cold water washing → drying.
For reactive dyes used in cold pad batch dyeing, dyes that are not too reactive but have a fast reaction speed should be selected. Generally, it is appropriate to choose dyes with moderate reactivity. This will help the pad dyeing solution maintain good stability. The process of cold pad batch dyeing is carried out at room temperature, and the diffusion of dyes in the dye liquor plays a decisive role in the dyeing rate. Therefore, the selected dye molecules are required to be smaller and easier to penetrate and diffuse. Fine fibers are used in production. Powdered dyes are better (p.f.f.d).
Since the dye liquor of cold pad batch dyeing is transferred to the interior of the fiber after padding the fabric, it is better to choose a dyeing department with low directivity. Level dyeing is easy to obtain. It is also helpful to overcome the phenomenon of light and dark hair tips, and the hydrolyzed dye can be easily washed away. However, in actual production, many factors such as dye solubility, color brightness, compatibility and price should also be taken into consideration for tracking and balancing.
2.1.2 Sample preparation
Sampling is cold pile dyeing A very important step before. The accuracy of the small sample directly affects the results of the large sample. For this reason,��Dye suppliers can offer a variety of solutions, many of which are quite simple. How to solve this problem in the future? The application of new technologies without rolling grooves and padding machines will undoubtedly play a role in this aspect.
4 Cold pile dyeing evaluation
1. Although the whole process is Semi-continuous, but because the preparation work is completed before going on the machine, the production efficiency is very high.
2. Dyeing and color fixing are completed at room temperature. Although water washing requires heating, cold dyeing has a high fixation rate and less hydrolyzed dyes, making it easy to clean. Pad dyeing with intermediate drying and steaming greatly saves water and steam energy and relieves the pressure of sewage decolorization.
3. Cold dyeing equipment is simple, requires less investment, and occupies a small area. Although it is stacked on the site after rolling, it can be flexibly arranged according to the workshop conditions.
4. Cold dyeing is not only easy to clean itself, but also allows planning and scheduling to allocate machines by color, saving the cleaning time of other machines due to frequent changes of varieties.
5. Since cold dyeing is slowly fixed at room temperature for a long time, migration will not occur. No matter the fabric is tight or thin, the permeability of the dye is excellent, so the color of the product is brighter. It is pure, completely solves the problem of corduroy bottoms, and meets market demand.
6. As long as the process is properly mastered, the problem of dyeing consistency of conventional colors, especially difficult colors, can be solved.
7. The cold-pile fabrics are stacked on the A-frame, which greatly relieves the turnover pressure of the fabric storage box.
8. Dyeing and cold dyeing also have problems such as seam head marks, hard feel, and lofting is not as intuitive as pad dyeing. </p
