The impact of conventional finishing on cloth surface
Finishing is the last step in the dyeing and finishing process. It is mainly responsible for processing gray cloth into products that meet the needs of various customers. The finished fabrics provide qualified clothing fabrics for garment factories. For yarn-dyed fabrics, the production process includes: singeing, desizing, mercerizing, washing, shaping, adding color, raising, sanding, calendering, resin, coating, and preshrinking.
1. Singeing: It mainly burns away the fluff on the surface of the cloth to make the cloth surface smooth and clean. It has little effect on the color of the cloth surface.
2. Desizing: The sizing on the gray fabric is removed through the action of enzymes and high-temperature water washing. It has little effect on the color of the cloth surface, but attention should be paid to the impact of the staining of the whitening agent on the color of some white cloths when they are desizing at high temperatures.
3. Mercerizing: Mercerizing uses the effect of concentrated alkali on cotton fibers to increase the luster and strength of cotton. It usually makes the cloth surface darker, and as the concentration of mercerizing alkali increases, the degree of darker cloth surface color also increases.
4. Washing: For fabrics containing BLUE R dye, the washing fastness of the dye is reduced due to the action of alkali after mercerization. In order to ensure the washing fastness of the finished product, finishing needs to be done after mercerization. Then wash with water. It can be seen that the fabric containing BLUE R dye will be lighter and less blue after washing.
5. Softening and styling: Some softeners have self-crosslinking properties and form a film on the surface of the fabric during styling, so they have a certain deepening effect, but the difference is not obvious. In addition, if the sublimation fastness of disperse dyes is not good at high temperatures, the color and fastness may be affected by the dye migrating to the surface.
6. Added color: For fabrics with a clear color or a nearly clear color whose color is significantly different from the standard, the color can be adjusted through jig dyeing.
7. Preshrinking: Preshrinking is a method of shrinking the fabric to meet customer requirements through mechanical action, and has little effect on the color.
The impact of alkali on cloth surface on finishing
Due to the gradual increase in water costs, cotton Cellulosic fiber fabrics such as cellulose fiber fabrics are more likely to have alkali on semi-finished gray fabrics before dyeing and finishing. Even in dyed finished products, the pH value of the cloth surface is above 8, and some even exceed 9; among them, The continuous long car pad dyeing production line is more frequent than the intermittent dip dyeing method.
The phenomenon of alkali in semi-finished gray fabrics after dyeing and before post-processing will have a greater adverse effect on many types of additives in post-processing and post-finishing, and sometimes even Very far-reaching (for example, some textile products dyed with reactive dyes that are not resistant to alkali hydrolysis will still have discoloration problems such as wind marks due to alkali on the fabric surface after a few months).
Because defects often appear during post-processing and finishing, this makes it easier to find the cause of the problem. It brings difficulties and easily leads to misleading and misjudgment, and the attention is blindly focused on post-processing, finishing aids, etc.
1. Impact on some post-processing additives
Post-processing generally refers to the completion of the dyeing process. The final steps include washing, soaping, color fixing (or cross-linking agent treatment), etc. For dyeing with reactive dyes, only after the floating color has been fully removed by soaping can the true and stable dyeing color be revealed. Fixing is done to improve intrinsic quality indicators such as color fastness. Although some fixing agents will cause a certain shift in hue and light, this should be controlled in advance during lofting work. Increasing color fastness is The first purpose of color fixation.
However, for some commonly used important fixing agents and cross-linking agents, most of the most suitable working bath pH values are weakly acidic at 5 to 6.5, and in alkaline media , the higher the pH value, the worse the effect. When the alkalinity reaches a certain level, precipitates may even precipitate.
Poor working conditions will not achieve the desired effect, so that indicators such as color fastness cannot be satisfactorily improved. At this time, even if the dosage of color-fixing agent or cross-linking agent is increased, the improvement in fastness is not synchronized, so the significance of increasing the dosage of additives is lost.
2. Impact of auxiliaries on finishing The last link in the big link, it is of great significance to the expansion of textile functions, extension of functions, and improvement of quality.
Some important additives in finishing, such as silicone softeners, non-iron resin finishing agents, etc., are also related to color fixing agents and cross-linking agents. In similar situations, it is more appropriate to process it in a weakly acidic working bath. The difference is that the taboo of silicone softeners is not that alkali agents can directly destroy the silicone oil that makes fibers soft, but that they can have a demulsifying effect on emulsified softeners.
Pure silicone oil cannot be used directly on textiles, so the emulsification method is used to make an emulsion (or microemulsion) with a silicone oil content of generally 10 to 15%. Only then can it become a commercial softener that is truly usable.
The alkali agent can demulsify the emulsified softener, causing the emulsifier to fail and silicone oil to precipitate. As time goes by, the separated and precipitated silicone oil points will become more and more demulsified. They gather again and form oil droplets with larger diameters that are visible to the naked eye. In severe cases, oil drifting may even occur.
After these separated silicone oils are stained on the fabric, they will form oil spots and blemishes of varying sizes. What’s more serious is that the organic silicone oil is firmly bonded to the fiber,The permeability of water to cellulose fibers is much better than that of cold water, so there is a saying that “the cheapest penetrant is hot water”.
Since hot water can improve solubility and promote permeability, it further improves and strengthens the basis for cleaning with alkali agents. Therefore, we can see that similar pre-treatment defects are often related to poor chemical materials and poor post-cleaning, and are often more likely to occur in winter.
Therefore, if the front-line truck operators do not have enough understanding of the water washing problem, they think that water washing has nothing to do with the overall situation and treat it casually, or even think that it has little impact on the color, in terms of water temperature, water volume, If the process parameters such as the number of washing times and washing time cannot be paid enough attention, the subsequent adverse effects will be difficult to avoid.
⑤ Due to the long-term treatment of the fabric in the working bath in the two major stages of pre-treatment and dyeing, the penetration and absorption of the alkali agent on the fiber has been extremely thorough. In continuous pad-dyeing production lines that are subject to extremely high tension, there is also a problem that surface cleaning is prone to occur, especially for some high-density and heavy gray fabrics. In this regard, in addition to strengthening cleaning, neutralization treatment is also a useful supplement.
It should also be noted that in addition to the variability of gray cloth and fiber types, changes in water quality, and failures in equipment and supporting facilities are all possible objective phenomena. Coupled with the possibility of subjective interference such as process execution, the alkali content of semi-finished gray fabrics will also be dynamic, and may often vary in levels and irregularities. For this reason, the regular detection and correction of the pH value of the rolling tank working bath should be set as a process procedure in on-site management.
Post-finishing is not only related to the change of color before and after dyeing, but also if corresponding measures are not taken after dyeing, the pH will be outside the normal range, causing quality problems, pH value It is one of the key conditions for chemical reactions, so it is also listed as one of the four major process conditions in dyeing and finishing production.
The alkali in dyed semi-finished products has a negative effect on many auxiliaries in post-processing and finishing. Although the mechanisms of their effects are different, they will produce sequelae. One thing is common.
The cause of alkali on semi-finished gray fabrics is, of course, related to washing, but different washing machines, process measures and washing efficiency effects are all related to it. Inextricably linked. This problem may seem like a trivial matter, but its negative impact is far-reaching. Many quality problems in dyed products are related to this problem, so it must be given full attention.
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