Foreword
Due to its loose structure, knitted fabrics are easy to deform, and rope-shaped fabrics are often used for dyeing and finishing. , low tension intermittent processing form. For the pre-printing and dyeing treatment of cotton knitted fabrics, intermittent processing with high-temperature alkali agents is currently basically used, which has problems such as high water and energy consumption, low dye vat utilization, hairiness and creases, and due to uneven processing quality. It has also become a potential source of instability in subsequent dyeing and finishing processing quality such as dyeing reproducibility and one-time success rate.
Although dyeing and finishing workers have improved the chemical industry by improving the parallelism of pre-treatment. Additive performance. The process structure has been continuously optimized, but for a long time, these problems have been looming in front of the knitting printing and dyeing industry and have become one of the common technical problems in the industry.
This article analyzes the impact of traditional in-cylinder pre-treatment of knitted fabrics on the dyeing and finishing quality of knitted fabrics, and proposes cold stack pre-processing of knitted fabrics in an open-width manner, combining scouring, Bleaching and dyeing are carried out separately, which is intended to take advantage of the uniform, stable and efficient advantages of open-width cold stack processing, and take into account the small change in the shape of knitted fabrics caused by low-tension processing, in order to obtain efficient and high-quality dyeing processing results.
The impact of traditional dye vat pre-treatment on knitted fabrics
1. Pre-treatment Influence of Treatment Uniformity For a long time, the pre-treatment method of knitted fabrics has been the intermittent processing method of rope-like high-temperature treatment in the dye vat. The fabric is scoured and bleached with strong alkali, scouring agent, oxidant and other auxiliaries. The time is generally 45 – about 60 minutes, and then clean, neutralize and remove oxygen. During this process, the rope-like running state of the fabric, the violent chemical reaction, and the cleaning effect after pre-treatment may be important reasons for the differences in treatment effects.
2. Influence of fabric operating status When the fabric is circulated in the dyeing machine in the shape of a rope , the fabric’s mechanical action points, heated hot spots and contact points with chemicals are different. In theory, as the position of the fabric continues to change, the fabric’s mechanical action points, heated hot spots and chemical action points will change accordingly. As time goes by, it will tend to be consistent, but in actual operation, the fabrics inside and outside the rope cannot be transformed evenly, so the transformation of the above-mentioned action points may be uneven. In addition, for the sake of saving energy and output, it is impossible to reduce this difference by extending the processing time without limit, which may result in differences in the degree of chemical reaction between the inner and outer rope fabrics and differences in washing neutralization. This treatment Differences in results may result in differences in dyeing and printing.
Note: If the fabric running time can be extended, the processing differences of this cylinder or cylinders will be greatly reduced.
3. The influence of the degree of chemical reaction. Under high temperature and alkaline conditions, the interaction between chemicals and fibers intensifies, and the controllability of hydrogen peroxide decomposition decreases and becomes Very lively, acting quickly and strongly on knitted fabrics. When there are differences in process condition control between dyeing machines or batches, it is difficult to eliminate the differences in cooking and bleaching between vats, resulting in inconsistent quality indicators of semi-finished products, which is also an important reason for dyeing vat differences. However, for a long time, the degree of oxidized cellulose produced by cellulose fibers under high-temperature alkaline conditions has often been ignored by dyeing workers. The direct result is that sensitive colors are difficult to control, the one-time success rate is low, and the cylinder difference is large. . Note: In the case of high-temperature cooking and bleaching in the machine cylinder without changing the conventional method, the changes in fiber chemical properties are almost impossible to balance, and the one-time success rate of dyeing sensitive colors has always been a matter of suspense.
4. Influence of cleaning effect In order to increase output and reduce production costs, many factories pursue shortening the processing time, and the time between the two processes is The washing process has naturally become the first choice for reduction or even removal. There are endless processes for reducing the washing process after pre-treatment, direct dyeing without draining, or even refining and dyeing in the same bath. The quality risks of fabrics dyed without removing residual chemicals are self-evident. In addition, pre-treatment quality problems caused by the technical performance of the equipment, the stability of the quality of the chemicals used, and the consistency of process condition control can all become the causes of dyeing and printing defects.
The impact of rope pre-treatment on knitted fabric production
1 There are many reasons for wrinkles in the process of rope boiling, bleaching, dyeing and dehydration. As we all know, the internal stress generated during the weaving process of cylindrical knitted fabrics will be released and eliminated during the printing and dyeing process. When the knitted fabric is running in the dye vat, on the one hand, the wet fibers swell through the action of high temperature and alkali agents, and the macromolecular segments are rearranged and adjusted; on the other hand, the fabric running in a rope-like manner is stretched in the length direction to form New tension
results in uneven deformation. When the tension in the fabric cannot be completely eliminated, wrinkles that are difficult to eliminate are produced. This problem can be improved but difficult to eradicate by reducing the tension during processing.
2. Fabric loss When knitted fabrics are processed in the rope shape, they are affected by mechanical effects such as water flow impact, long-term impact and friction with the cylinder, and the fabric will inevitably produce loss. The effects of chemicals and high temperatures aggravate this loss, and the longer it takes, the more severe the loss of the fabric will be.
3. The production capacity of the dye vat. The design optimization of the dye vat is mainly focused on dyeing efficiency and uniformity. The design of low liquor ratio vapor mist and liquid flow dye vats reflects the wisdom of design experts. , but in terms of pre-treatment and cleaning, it does not have a significant effect compared with the large liquor ratio dye vat. If the pre-treatment is completed through standardization outside the vat, the dye vat does not need to be limited by the pre-treatment effect and focuses on the special control of dyeing, which not only improves the quality level of dyeing but also improves the utilization rate of a single vat, giving full play to its high efficiency advantage. , the same number of dye vats can increase production capacity by 30-50%.
4. Consumption of energy resources. With the rising prices of energy resources and social and environmental pressures, enterprises’ awareness of energy conservation and environmental protection has been continuously strengthened, so the optimization of processes has also increased. On the agenda, the traditional cooking and bleaching method also faces challenges. In the absence of new process methods, companies often choose low liquor ratio dye vats to complete the pre-treatment and dyeing processes. However, in actual use, the pre-treatment and cleaning of fabrics are energy-saving. It is not very significant. There is still great potential to be tapped in view of the current economic goals of energy conservation and emission reduction.
Open-width cold pile continuous pre-treatment technology
Open-width cold pile continuous pre-treatment developed according to the characteristics of knitted fabrics Technology, using the method of “loose immersion, flat stacking, and tension-free steam cleaning”, can realize the refining and bleaching processing of cotton knitted fabrics, effectively overcoming problems such as uniformity of treatment results and stability of fabric shape. This technology can change the traditional intermittent production mode of quantitative cylinder feeding into a semi-continuous production mode. It adopts low-temperature stacking and short-term steaming technology, which has significant energy saving and emission reduction effects.
1. Open-width loose immersion, flat stacking, tension-free steaming and cleaning using “immersion treatment solution – room temperature stacking – short steaming – – The new process route of “normal temperature continuous flat washing”. The knitted fabric passes through the padding car or the spray liquid feeder in the open width under normal temperature conditions, and the pretreatment additive is applied to the fabric in a certain amount of liquid in the open width to seal it. The stacking method is sealed and stacked at room temperature for 4/hour, and then steamed continuously for 10 minutes at 95°C in a steaming box, and then subjected to continuous open-width countercurrent aeration water washing and convection spray washing at room temperature, and then the cloth is dropped. High efficiency and low consumption can be obtained. processing effect.
2. The cold stack equipment technology uses synchronous variable frequency active rotation of the pressure roller and electronic pressure measurement control to ensure loose processing of knitted fabrics, avoid dead wrinkles, and ensure that the fabric of relaxation and smoothness.
3. Intelligent control technology adopts advanced sensing technology to realize online monitoring and automatic adjustment of process parameters.
4. Special cold pile processing additives are applied to develop special additives with the characteristics of “rapid penetration, uniform decomposition, excellent emulsification and saponification dispersion, environmental protection and mildness” to effectively solve the problem Solve the problem of uniform penetration of textile auxiliaries under low force.
Characteristics of open-width cold reactor pre-treatment technology
1. The fabric is running in open width. The fabric is open-width with liquid, and the treatment liquid penetrates evenly. It is stacked flatly without wrinkles and imprints, and good flatness is maintained. Open width steaming and 7 water washing can make the fabric react completely and wash thoroughly and evenly.
2. The soft, uniform and strong penetrating agent ensures rapid penetration of chemicals into the fabric, ensuring that the liquid inside and outside the fiber is consistent, and the chemical properties of the treatment liquid under normal temperature conditions are relatively stable. , does not change much in continuous operation, and the treatment liquid has a gentle and uniform effect on the fibers, thus minimizing inter-batch quality differences.
3. Chemical reactions are controllable. During the sealed stacking process at room temperature, scientifically formulated chemicals and effective decomposition of hydrogen peroxide can be well controlled, and the refining process It is gentle, uniform and thorough, with little damage to the fiber, uniform hair effect at each point, and no decrease in fiber physical indicators. It overcomes the quality difference of pre-treatment in the dye vat and improves the reproducibility and first-time success rate of dyeing.
4. The low tension in the whole process realizes the low tension operation of the fabric in the whole process of padding, stacking and steam washing. The fibers can be flat and relaxed. It fully swells and releases internal stress under certain conditions, which completely solves the problem that fabrics easily produce wrinkles due to different tensions in the cylinder, and has a better hand feel.
5. Fabric quality and energy-saving and emission-reduction processing of cotton knitted fabrics has a whiteness of more than 80%, a wool effect of 8 cm/30min, and a smooth fabric with few wrinkles. , high dyeing reproducibility, pH value of cloth surface after washing is neutral, fiber loss is 1-2% lower than traditional hot bleaching process, waste water discharge is reduced by more than 40%, steam consumption is saved by more than 80%, and electricity consumption is saved by more than 40% , The effect of energy saving and emission reduction is very significant.
Editor’s Note
The effective use of the cold stack continuous pre-treatment method of knitted fabrics enables the scouring and bleaching of cotton knitted fabrics to get rid of the traditional intermittent method The constraints of the processing method are separated from the dye vat, and the processing effect is stable and excellent. The continuous, standardized, and professional production process achieves high reproducibility, high success rate, and high flatness of dyeing, effectively increasing the production capacity of the dye vat, and fully It leverages the advantages of dyeing vat dyeing design and achieves energy saving and emission reduction in the pre-treatment and dyeing stages, which is of great significance to the sustainable development of my country’s knitting printing and dyeing industry.
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