The quality of pre-treatment (scouring and bleaching) is not only related to the quality of finished bleached products, but also directly affects the quality of dyeing, printing, finishing and other semi-finished products. Some experts say that 70% of quality problems in dyeing and finishing products are caused by poor pre-treatment. There is a certain reason for this. The quality of dyeing and finishing is related to gray fabrics, equipment conditions and operations, process technology and execution, and dyes. , it is also related to auxiliaries, we focus on the influence of auxiliaries.
01 Common quality problems and additive selection in pre-treatment
1. Problems of poor whiteness and wool effect
Whiteness Poor quality includes impure and uneven whiteness and the wool effect cannot reach more than 8cm in 3Omin. This is related to the quality of the knitted fabric. For example, if there is a lot of low-grade cotton, it is often difficult to achieve good whiteness and wool effect. Of course, the most important thing is the process formulation. And the problem of auxiliary selection, the amount of H2O2 and NaOH must be sufficient in the process formulation:
H2O2 not only plays the role of bleaching pigments in pretreatment, but also has the function of removing impurities (including (Removing cottonseed hulls), the amount of H2O2 is insufficient (including decomposing too quickly), and the whiteness cannot be guaranteed; NaOH not only provides the alkali (pH) required for H2O2 bleaching, but also cooperates with the scouring agent to maximize the impurity removal effect. The amount of NaOH If it is not enough, impurity removal will be poor, and the gross effect will not meet the requirements first. Of course, the whiteness cannot meet the requirements, so the amount of H2O2 and NaOH can be said to be the primary factor in ensuring whiteness and wool effect.
Choose high-quality scouring agents:
The comprehensive effects of scouring agents such as cleaning, emulsification, dispersion, and penetration must be excellent to ensure that impurities are completely removed and ensure Whiteness and gross effect, but the quality of scouring agents on the market is uneven. We must choose products with excellent comprehensive effects instead of just measuring penetration and solid content. Penetration is only one aspect to consider.
Oxygen bleaching stabilizer and chelating dispersant:
These two additives are mainly used to improve the essence, adsorb and complex Fe3+ and other metals in the water ions to prevent the rapid and ineffective decomposition of H2O2 catalyzed by metal ions. If H2O2 decomposes quickly and ineffectively, the whiteness and wool effect will not meet the requirements, and the fabric will be brittle and even have holes. Therefore, in order to achieve whiteness and wool effect, excellent oxygen bleaching stabilizers must be selected, and the decomposition rate of H2O2 must be considered during the selection. The addition of chelating dispersant not only chelates iron, etc., but also chelates and disperses various impurities in the water, so that these impurities will no longer contaminate the fabric again and cause dark whiteness and graying. Therefore, chelating dispersant not only Both its chelating power for metal ions and its dispersion power should be considered.
Process conditions:
It takes a certain amount of time and temperature to allow the additives to react with impurities. If the conditions are not met, the pigments and impurities will not be completely removed. , the whiteness and hair effect cannot be achieved either.
Washing:
Washing after scouring and bleaching is very important. It is necessary to clean the removed impurities to ensure whiteness and wool effect.
2. The cottonseed hulls are not completely removed
The removal of cottonseed hulls mainly depends on the expansion and swelling of cottonseed hulls by NaOH under certain conditions, and then after a certain period of time Mechanical cleaning power removes cottonseed husks. Incomplete removal is mainly caused by insufficient temperature and time. Therefore, sufficient time must be given at a certain temperature to completely remove cottonseed husks. H2O2 and scouring agents are helpful in removing cottonseed husks, so in There must be a certain temperature and time in the pretreatment to ensure the removal of cottonseed hulls. At the same time, NaHSO3 or anthraquinones can be added to help remove cottonseed hulls.
3. Holes and brittle damage
The causes of holes and brittle damage include singeing holes, scratches during processing, and original gray cloth In addition to holes and other causes, the main reason is the presence of Fe3+, Cu2+ and other metal ions in the H2O2 bleaching bath or on the cloth surface; these metal ions catalyze the rapid decomposition of H2O2, causing brittle damage to the fiber. If metal ions (such as rust, etc.) are too concentrated in one place, the fibers and yarns will become brittle and form holes. Therefore, in H2O2 bleaching, high-quality oxygen bleaching stabilizers and chelating dispersants must be selected to complex and absorb the fabric and The metal ions in the bleach bath prevent H2O2 from decomposing too quickly and causing holes or brittle damage. Of course, alkali on the cloth surface (the alkali removal is not clean) or acid (the acid removal is not clean) will also cause brittle damage. At the same time, under high temperature and alkali conditions, the fabric will be brittle and damaged when there is air. This situation can be prevented by adding weak reducing agents such as NaHSO3.
In addition, moisture and mildew in fabrics are also one of the causes of brittleness and holes.
02 Common quality issues in dyeing and selection of auxiliaries
1. Unqualified color fastness
Color fastness to sunlight Fastness, soaping fastness, perspiration fastness, rubbing fastness, blooming fastness, ironing fastness, etc. The key to these fastnesses lies in the structural properties of the dye, and is also related to the fiber, dye concentration, dyeing and finishing process, External conditions are closely related, so the key to whether the color fastness reaches the standard is the selection of dyes, followed by the dyeing process and the application of auxiliaries.
When producing a dyeing process certificate, it must be reasonably determined based on the dye, fiber and customer indicators, so that the dye, with the help of additives, can dye the fiber as firmly as possible under certain conditions and fully fix it. For auxiliaries, one is to use good leveling agents and dye accelerators to make the dye slowly, evenly and fully dye the fibers; the other is to add chelating agents to overcome the floating color caused by the complexation of the dye with metal ions in the water, and Reduce the hydrolysis of reactive and other dyes in water; the third is to choose an excellent soaping agent to remove floating colors and prevent floating colors from re-staining the fabric; the fourth is to choose an appropriate fixing agent, which currently has a negative impact on sublimation fastness and sun fastness. There is no degree yetThe original tar-like softener and other substances fell off and stuck to the fabric.
Silicon oil stains
Silicon oil stains are the most difficult type of stains to treat. The main reasons are:
(1) The pH value of the cloth surface is not neutral, especially with alkali, causing the silicone oil to break and float;
(2) The water quality of the treatment bath is too poor, the hardness is too high, and the silicone oil is larger than It is very easy for oil to float in water with a hardness of 15Omg/L;
(3) Silicone oil quality issues include poor emulsification (poor emulsifier selection, poor emulsification process, too large emulsified particles, etc.), Shear resistance (mainly problems with the silicone oil itself, such as silicone oil quality, emulsification system, silicone oil types, silicone oil synthesis process, etc.). You can choose silicone oil that is resistant to shear, electrolytes, and pH changes, but you should pay attention to the use method and environment of the silicone oil. You can also consider choosing hydrophilic silicone oil.
Poor raising
Poor raising is closely related to the operation of the raising machine (such as tension control, raising roller speed, etc.) Relationship, for fluffing, when applying softener (commonly known as waxing), controlling the dynamic and static friction coefficients of the fabric is key, so the preparation of fluffing softener is the key. If the softener is not used properly, it will directly cause poor fluffing. , or even cause breakage or door width changes.
2. Common quality problems in resin finishing
Formaldehyde problem
Due to the free Formaldehyde or formaldehyde decomposed from resin with N-hydroxymethyl structure causes formaldehyde content to exceed the standard. Ultra-low formaldehyde resin or formaldehyde-free resin should be used.
Of course, formaldehyde problems come from a wide range of sources, such as color fixing agents Y and M, softeners MS-20 and S-l, waterproofing agents AEG and FTC, adhesives RF, flame retardants THPC and other additives. It can also cause formaldehyde to exceed the standard. At the same time, formaldehyde migration in the air may also cause formaldehyde on fabrics to exceed the standard.
Yellowing or discoloration problems
After resin finishing, yellowing will generally occur, so: Reduce yellowing as much as possible Yellow, discoloration.
The problem of strength decrease
General resin finishing will cause strength decrease. Fiber protective agents, such as oxidized polyethylene wax, can be added. emulsion body.
Feel problem
Generally resin finishing will cause the feel to become hard. Soft ingredients can be added, but care should be taken not to affect the resin. Finishing quality. The hand feel has improved, and the problem of power drop has also been greatly improved. However, problems such as a hard feel caused by surface resin are caused by the resin itself and drying, and need to be improved accordingly.
3. Other quality problems
Metal ions exceeding the standard
Metal ions Cu, Cr, Co, Ni, Zn, Hg, As, Pb, Cd, etc. need to be tested in export products. If they exceed the standard, they will have serious consequences like formaldehyde exceeding the standard. Among the additives, there are relatively few metal ions of this type, but some additives can cause exceeding the standard. For example, the flame retardant antimony trioxide emulsion contains a large amount of mercury, and the waterproofing agent CR, phoboTexCR (Ciba), Cerolc (Sandoz), etc. chromium. When using mordant dyes on wool, the mordant dye used is potassium dichromate or sodium dichromate or sodium chromate, and Cr6+ will exceed the standard.
The problem of color changes
After finishing, there are many problems of color changes. This must be paid attention to the dye during dyeing. When dyeing, you must carry out corresponding finishing according to the process to determine whether the selected dye will change color under the action of additives. Of course, it is best to choose a finishing agent that will not cause color change. solution, but this often has limitations (for example, the copper-containing antibacterial agent itself has a color, and the chromium-containing waterproofing agent also has a color, which will cause discoloration of the fabric). At the same time, it is also necessary to consider the sublimation of the dye when the dyed fabric is dried and baked. Factors such as light color and discoloration and yellowing caused by excessive temperature.
APEO exceeds the standard
APEO is also strictly restricted by some countries as an indicator. This indicator and the refining agent in pre-treatment , penetrants, cleaning agents and leveling agents in printing and dyeing, emulsifiers in softeners during finishing, etc. are all related. At present, TX and NP series surfactants are widely used as auxiliary raw materials. Prevention is difficult, but the only way is for printing and dyeing factories to insist on using environmentally friendly additives and strictly prevent additives containing APEO and toxic and harmful substances from entering the factory.
There are many common quality problems in dyeing and finishing products, and there are many reasons for them. Some quality problems cannot even be analyzed. Here we only discuss the relationship with auxiliaries and communicate with peers. If there is anything inappropriate, please invite experts. Peers make corrections. </p
