Due to its loose structure, knitted fabrics are easy to deform, so their dyeing and finishing processes mostly use rope-shaped, low-tension intermittent processing. For the pre-printing and dyeing treatment of cotton knitted fabrics, intermittent processing using high-temperature alkali agents is currently basically used. Not only does it have problems such as high water and energy consumption, low dye vat utilization, hairiness and creases, but also due to poor processing quality. Uniformity 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 improve the performance of chemical additives by improving the parallelism of pre-treatment. 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-treatment of knitted fabrics in an open-width manner, combining scouring, bleaching and The dyeing is carried out separately to take advantage of the uniform, stable and efficient advantages of open-width cold stack processing, and to take into account the small change in the shape of knitted fabrics due to low tension processing, in order to obtain efficient and high-quality dyeing processing results.
1. The impact of traditional in-tank pre-treatment on the quality of knitted fabric dyeing and finishing
1. Influence of pre-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, using strong alkali, scouring agent, oxidant and Other auxiliaries are used to scouring and bleaching the fabric, usually for about 60 minutes, and then cleaning, neutralizing and deoxidizing. 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.
(1) Influence of fabric operating status
The fabric is When the fabric is circulating in the dyeing machine, the mechanical action points, heating points and contact points with chemicals are different. In theory, as the position of the fabric continues to change, the mechanical action points and heating points of the fabric will change. The action points of chemicals will tend to be consistent over time, but in actual operation, the fabrics inside and outside the rope cannot transform evenly, so the transformation of the above 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.
(2) Influence of the degree of chemical reaction
At high temperatures and Under alkaline conditions, the interaction between chemicals and fibers intensifies, the controllability of hydrogen peroxide decomposition decreases, and it becomes very active, with a rapid and strong effect 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: During high-temperature cooking and bleaching in the cylinder without changing the conventional method, the change in fiber chemical properties is almost the same. Unable to achieve balance, the one-time success rate of dyeing sensitive colors is always in doubt.
(3) Impact of cleaning effect
In order to increase production In order to reduce production costs, many factories are pursuing shortening the processing time, and the washing process between the two processes has naturally become the first choice to reduce or even eliminate it. The washing process after pre-treatment is reduced, and the washing process is directly dyed without draining. There are even endless techniques for practicing dyeing and bathing together. The quality risks of fabrics dyed without removing residual chemicals are self-evident.
In addition, due to the technical performance of the equipment, the stability of the quality of the chemicals used and the consistency of process condition control, etc. Pre-treatment quality problems can become the cause of dyeing and printing defects.
2. The influence of rope pre-treatment on the smoothness of knitted fabrics
There are many reasons for wrinkles during 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, difficult problems arise. Eliminate wrinkles. This problem can be improved but difficult to eradicate by reducing the tension during processing.
3. Fabric loss
When knitted fabrics are processed in the form of ropes, they will inevitably suffer from mechanical effects such as water flow impact, long-term impact and friction with the cylinder, etc.
�The effects of chemical agents and high temperature aggravate this loss, plus 1: the longer the time, the more serious the loss of the fabric.
4. The production capacity of the dye vat
The design optimization of the dye vat is mainly focused on dyeing efficiency and uniformity, and the design of low liquor ratio aerosol and liquid flow dye vats reflects the design experts Wisdom, but it does not have a significant effect on pre-treatment and cleaning compared to a 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%.
5·Consumption of energy resources
With the rising prices of energy resources and social and environmental pressures, enterprises’ awareness of energy conservation and environmental protection continues to strengthen, so the optimization of processes is also on the agenda. The traditional boiling and bleaching methods are also facing challenges. In the absence of new process methods Enterprises mostly use dye vats with low liquor ratio to complete the pre-treatment and dyeing processes. However, in actual use, the energy saving in pre-treatment and cleaning of fabrics is not very significant. Take a dye vat of 1:5-1:8 as an example to process one ton of fabric. The steam consumption is 1.5 tons and 2.5 tons, the water consumption is 25 tons and 35 tons, and the electricity consumption is 150 degrees and 120 degrees. In view of the current economic goals of energy conservation and emission reduction, there is still great potential to be tapped.
2. The application of open-width cold pile continuous pre-treatment technology in knitted fabric pre-treatment Application
The open-width cold pile continuous pre-treatment technology developed according to the characteristics of knitted fabrics adopts “loose immersion, flat The method of “type stacking, tension-free steaming and washing” can realize the scouring 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
This process adopts “immersion treatment solution-room temperature stacking-short steaming-normal temperature continuous flattening” The new process of “washing”, the knitted fabric passes through the padding car or the spray liquid feeder in the open width mode under normal temperature conditions, and the pretreatment additive is applied to the fabric in the open width mode with a certain amount of liquid, and the sealing layer is stacked at room temperature. The sealed pile 2 is placed for 4 hours, and then steamed continuously for 10 minutes at 95°C in a steaming box, and then washed with continuous open-width countercurrent aerated water and convection spray washing at normal temperature and then dropped into cloth. This can achieve high-efficiency and low-consumption treatment results.
2. Special cold stack equipment technology
Using synchronous variable frequency active rotation of pressure rollers and electronic pressure measurement control to ensure loose processing of knitted fabrics, avoid dead wrinkles, and ensure the relaxation and smoothness of fabrics.
3. Intelligent control technology
Adopts advanced sensing technology to realize online monitoring and automatic adjustment of process parameters.
4. Application of special cold stack treatment additives
Develop special additives with the characteristics of “rapid penetration, uniform decomposition, excellent emulsification and saponification dispersion, environmental protection and mildness”, which effectively solves the problem of textile problems under low force The problem of uniform penetration of additives.
3. Characteristics of open-width cold reactor pretreatment technology
1. Fabric open-width operation
The fabric is open-width with liquid, the treatment liquid penetrates evenly, and is stacked flat without wrinkles and imprints, maintaining good flatness. Open width steaming and 7 water washing can make the fabric react completely and wash thoroughly and evenly.
2. The effect is soft and uniform
The strong penetrating agent ensures rapid penetration of chemicals into the fabric, ensuring that the liquid inside and outside the fiber is consistent. The chemical properties of the treatment liquid under normal temperature conditions are relatively stable, and during continuous operation There is little change, and the treatment liquid has a gentle and uniform effect on the fibers, thus minimizing batch-to-batch quality differences.
3. The chemical reaction is controllable
During the sealed stacking process at room temperature, the effective decomposition of hydrogen peroxide can be well controlled by scientifically formulated chemical agents. The refining process is gentle, even and thorough, and the The fiber damage is small, the wool effect at each point is uniform, and the physical index of the fiber does not decrease. It overcomes the quality difference of pre-treatment in the dye vat and improves the reproducibility and first-time success rate of dyeing.
4. Low tension in the whole process
It realizes the low tension operation of the fabric in the whole process of padding, stacking and steam washing. The fibers can be fully swollen and released under flat and relaxed conditions. The internal stress completely solves the problem of wrinkles caused by different tensions in the cylinder, and the hand feeling is better.
5. Fabric quality and energy saving and emission reduction
The cotton knitted fabric processed by this technology has a whiteness of more than 80%, a wool effect of 8 cm/30min, the fabric is smooth and wrinkled, and the dyeing is reproducible High resistance, pH value of cloth surface after washing is neutral, fiber loss is reduced by 1-2% compared with traditional hot bleaching process, waste water emission is reduced by more than 40%, steam consumption is saved by more than 80%, electricity consumption is saved by more than 40%, energy saving and emission reduction The effect is very significant.
Conclusion
Knitted fabrics are cold The effective use of the continuous pre-treatment method enables the scouring and bleaching of cotton knitted fabrics to get rid of the constraints of traditional intermittent processing methods and be separated from the dye vat. The treatment effect is stable and excellent, and the production process is continuous, standardized and professional to achieve dyeing. The high reproducibility, high success rate and high smoothness effectively increase the production capacity of the dye vat, give full play to the advantages of dye vat dyeing design, achieve energy saving and emission reduction in the pre-treatment and dyeing stages, and are important for the sustainable development of my country’s knitting printing and dyeing industry. of great significance.
�The constraints of the method are separated from the dye vat, and the treatment effect is stable and excellent. The continuous, standardized and professional production process achieves high reproducibility, high success rate and high flatness of dyeing, effectively improving 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. </p
