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 the fabric 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 it is necessary to use emulsification method to make an emulsion (or microemulsion) with a silicone oil content of generally 10 to 15%, in order to become a truly usable commercial softener.
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. When these separated silicone oils are stained on fabrics, they will form oil spots and blemishes of varying sizes. What’s more serious is that the silicone oil is firmly combined with the fiber, making the removal and repair of such defects difficult.”Water”. Since hot water can improve solubility and promote permeability, it further improves and strengthens the basis for cleaning alkali agents. Therefore, we can see similar defects in pre-treatment, and Poor chemicals and poor cleaning afterwards are often related, 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. If you treat it casually, even thinking that it has little impact on the color, and do not pay enough attention to the process parameters such as water temperature, water volume, number of washing times, washing time, etc., the negative consequences 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, and the continuous tension on the gray fabric is extremely great. In the pad-dyeing production line, there is also a problem that surface cleaning is easy to occur, especially for some high-density and heavy gray fabrics. In this regard, in addition to strengthening the 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 of the semi-finished gray cloth will also be dynamic, and may often vary irregularly. For this reason, the pH value of the rolling tank working bath must be adjusted in on-site management. Regular detection and correction should be set as process procedures.
Post-finishing is not only related to the color changes before and after dyeing, but also if corresponding measures are not taken after dyeing, Leading to abnormal pH range and quality problems. PH value 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 of dyed semi-finished products is important for post-processing and Many additives in finishing have negative effects. Although the mechanisms of their effects are different, they are common in that they will produce sequelae. The cause of alkali on semi-finished gray fabrics, superficially, is of course related to It is related to water washing, but different washing machines, process measures and washing efficiency effects are inextricably linked to it. This problem may seem like a small matter, but the negative consequences are wide-ranging, and many dyed products have quality problems. They are all related to this, so they must be given full attention.</p
