Analysis Of Common Problems Of Textile Fabrics Failing The Test And How To Solve And Improve Them!

There are two common aspects of the test items, one is the physical project and the other is the chemical project. The chemical project is also what we call environmentally harmful substances. Let's first understand a piece of data. These data have also been compared by ITS and BV in the three major testing institutions, which basically coincide with the situation we encountered.

The proportion of test items that failed:

1. Six-fiber fastness (including washing, sweat stains, water stains and six fibers) accounted for 32% of the failures

2. Anti-pilling accounted for 16%

3. Wet grinding fastness 11%

4. Sun fastness 9%

5. pH value 7%

6. Twist and shrinkage 5%

7. Environmentally harmful substances (azo formaldehyde apeo pcp heavy metals) 1.5%

8. Others

This is basically consistent with our current actual production. Among them, color fastness accounts for almost half, and pilling, light fastness, pH, twist of knitted fabrics, and shrinkage all account for a relatively large proportion. There is also an environmentally friendly substance, which seems to account for a small proportion, but once the fabric has environmental problems, it will have a relatively large impact on the entire bulk product. Since these items are so difficult to pass the test, we have to explore the problem and how to solve and improve it?

The first reason for failing the test: customer standards are getting higher and higher. For example, the washing fastness was basically qualified at level 3 a few years ago. Now many test reports require level 3-4. Level 4, and we even encounter some customers who ask for level 5. For such orders, we can only shake our heads. There are also environmental issues, such as apeo content. No one paid attention to it at the beginning, and the test did not require it. If there is a requirement, it is within 300ppm. Now customers require less than 100ppm, less than 50ppm, or even less than 10ppm.

Start with the most common washing six-fiber fastness.

Washing fastness of six-color fiber

1. Washing fastness is to test the color change of fabric and six kinds of fiber strips in a certain temperature and a certain amount of soap solution in the same bath. The color change before and after washing is called washing discoloration. The degree of adhesion of the washed dye to the six kinds of fibers is graded by gray card, which is called staining fastness. Wool, acrylic, polyester, nylon, cotton, diacetate fiber. Generally, polyester, cotton, and nylon will not have any problems. Our dyeing factory can achieve 3-4 or above. Many dark colors we see can achieve 4 levels. However, we found that all polyester and spandex fabrics and their blended fabrics are put together to dye medium and dark colors. Washing is generally not good. Why? This is because polyester disperse dyes are very serious for spandex staining. When we use insurance powder and soda ash for reduction cleaning, the surface floating color on polyester can be basically cleaned, but the staining on spandex cannot be cleaned. Therefore, more often, our polyester + spandex products have medium and dark washed six-fiber staining at about 2-3 levels.

Moreover, dyeing factories prefer high temperatures for the final shaping of finished products. Disperse dyes will sublimate when the temperature exceeds 140 degrees. This is why we need to set them at low temperatures in the last process when making high fastness.

The washing fastness of polyester + nylon fabrics is also not good. Why? When dyeing nylon and polyester, light colors with quick dyes or mostly with disperse dyes will cause serious staining of nylon. These stains cannot be improved by fixing the color, and washing will cause a large color change. Therefore, the dark color fastness of nylon and polyester fabrics is still a pain point in the industry.

There is also a common suede fabric, scientifically known as sea island silk, which is also a kind of polyester. The fiber opening process is generally not ideal, and the fiber cannot fully open the pores, and the crystallization changes become lower. Therefore, when dyeing, the concentration of owf is much higher than that of conventional polyester under the same color depth, and the dye concentration is also much higher. Its medium and dark colors are not so much dyed, but we describe it as the color piled up by the dye. This floating color is very serious, and the washing color fastness is mostly at level 1.5, level 2, and level 2.5. Some of the dyeing factories in Fujian and Guangdong can achieve grade 3 and grade 3-4 if the fiber opening process is done well.

Other polyester-cotton, nylon-cotton and other fabrics can basically meet the requirements through correct soap washing, color fixing and double-fixing washing fastness. Our high fastness is basically polyester + spandex products that need to choose high fastness dyes.

2. Friction fastness. Everyone is familiar with friction fastness, which is: dry grinding and wet grinding. There are very few friction problems with polyester and nylon fabrics. Most of them are cellulose fibers such as cotton, rayon, linen and their blended products. There will be friction problems in the dark colors. This is determined by the characteristics of the reactive dyes they use for dyeing. Reactive dyes form covalent bonds with fibers during dyeing. If dry grinding is not good, we can judge whether the cloth has floating color. It can be solved by fixing and soap washing. Wet grinding is because reactive dyes are easy to fall off under certain pressure and humidity, so the wet grinding of fiber cotton, rayon and linen fabrics is basically around grade 2.5. This is solved by the nature of reactive dyes.

Improvement plan: First: Pre-treatment should be sufficient, color absorption is more uniform, and fastness is better. Second: Strengthen soap washing and clean floating colors. If you want to achieve wet grinding level 3 or above, you can add wet grinding enhancer during shaping. This product is now relatively mature, and it basically improves half a level to one level.

3. pH value pH is commonly known as acidity and alkalinity. It is expressed by numbers 1-14. The middle value 7 is neutral, and below 7 is acidic. The smaller the number, the greater the acidity. Above 7 is alkaline, and the larger the number, the stronger the alkalinity. 18401 standard a class 4-7.5 is considered qualified, but now many of our customers' corporate standards set pH at 5.5-7.5, and some are set between 6-7. This will be more difficult to achieve for large quantities. Now let's analyze why the pH of our fabrics does not meet the requirements: This needs to be understood from the last process of our dyeing:

For example, polyester is dyed under acidic conditions, but when reducing and cleaning, it is necessary to add insurance powder and soda ash to clean the floating color, and then use ice vinegar to adjust the pH before leaving the vat. Ice vinegar is relatively acidic and the pH adjustment is unstable, so in many cases the pH after dyeing is alkaline around 8-9, or the ice vinegar is too acidic and does not meet the standard.

Cotton, rayon, linen and blended fabrics need to be dyed with soda ash during active dyeing. The dye forms a covalent bond with the fiber, and the soaping agent used for soaping is also weakly alkaline. Finally, ice vinegar is used to adjust the pH before leaving the vat. In the same situation as polyester, the unstable pH adjustment of ice vinegar can easily cause the pH to be alkaline or the ice vinegar is too acidic and does not meet the standard. There are also dyeing factories that simply do not adjust the pH before leaving the vat, and use citric acid to adjust it in the setting machine, which will cause the pH to be unstable or the feel will not be soft.

Nylon and blended fabric dyeing factories will put nylon dyeing last. Dyeing is done under acidic conditions and color fixing is also done under acidic conditions. Therefore, the nylon fabric has a pH of about 4-6.5, which is less problematic. Excessive acidic color fixing agents may also cause the pH to be below 4.

Conclusion: The pH can be adjusted to within the requirements of 4-7.5 or 5.5-7.5 with ice vinegar after professional calculation before leaving the vat. However, many of our dyeing factories now rely on the experience of color masters to adjust, so there will be some errors. For some sensitive light colors such as bleached colors or light yellow and light green, which are prone to yellowing or discoloration after leaving the vat, we will also use a color protector, which can keep the color from changing color when placed and fixed, and can also adjust the pH to between 5-7.5

4. Torsion Torsion is the internal stress of the fabric itself, and the degree of deformation after washing, also known as twist.

Twist test method: ac – bd/ac + bd (2) Positive value means left skew, negative value means right skew

Weaving reason: The more reasonable the specifications of the grey cloth, the less likely it is to produce skew. The finer the yarn count, the easier it is to produce skew.

Improvement plan: When determining whether the skew of a fabric meets the standard, we can make a pre-set version, calculate the twist based on the s skew and z skew, and then adjust it by setting the weft beating angle. The second twist is that the pants do not twist the legs. This is for the pants material. It is also necessary to test whether the fabric is twisted. If it is, it is necessary to make the fabric tilted first, and then twist it back when washing.

5. Sunlight fastness

National standard for sunlight exposure European standard 8-level system, level 1 is the worst, level 8 is the best, and the American standard is 5-level system, level 1 is the worst and level 5 is the best

1) Factors affecting failure

Fabric structure

Dye molecular structure (dye is the most critical)

Use dyes with different sunlight fastness to match colors

Some auxiliaries treated on fabrics will affect sunlight fastness (such as fixing agent softener)

Most fluorescent colors are generally worse than 2 levels in sunlight exposure, and many colors of paper printing are worse than 2-3 levels in sunlight exposure. Colors are sensitive and have poor sunlight fastness, such as gray, green, etc.

2) How to improve

Correctly select dyes

Formulate and implement reasonable dyeing process conditions, and pre-treatment to fully dye the fabric evenly and thoroughly, and fully fix the color; Soap and wash after dyeing to fully remove floating color and use light fastness enhancer

6. Pilling performance

There are four common ways of pilling: Martindale 2000, box pilling, random flipping, circular trajectory. Different test methods will produce different results.

Pilling process

Pilling: The fiber ends are pulled out of the fabric due to friction to produce long pile; the single filaments in the filaments are broken and hooked out to form a wire loop

Pilling: The fibers that have not fallen off are entangled with each other, and the more they are entangled, the tighter they are, and finally small pellets are formed

Reason

Fiber properties: The fibers have high strength and high elongation, especially fatigue-resistant fibers are prone to pilling

Yarn structure: When the yarn twist is large, the large fibers in the yarn are bound very tightly, and the fibers are not easy to be pulled out and pilling

Fabric structure: Plain fabrics are least likely to pilling, satin fabrics are most likely to pilling, and knitted fabrics are more likely to pilling than woven fabrics

Improvement tips: Choose yarns with good twist and less hairiness, which are not easy to pilling. The tighter the fabric, the less likely it is to pilling. Appropriate singeing, shearing and brushing can reduce the pilling performance of the fabric. Excessive softness has a certain detwisting effect, which will increase the risk of pilling. Enzyme treatment and anti-pilling finishing can improve the anti-pilling performance to a certain extent.

7. Color fastness to bleaching and non-chlorine bleaching

1) Factors affecting failure

Active chlorine reacts with dyes, causing oxidative decomposition of dyes;

Peroxide reacts with dye matrix, causing dyes to change color or fade, or destroying the combination of dyes and fibers.

The color fastness of dyes to chlorine bleaching and non-chlorine bleaching is related to the dye structure, and generally reactive dyes are generally poor.

2) How to improve

Reasonably screen dyes and choose dyes with chlorine bleaching and non-chlorine bleaching structures; (Reactive dyes are generally poor, and vat dyes are the best)

Fully scour before dyeing and fully wash after dyeing, strive to remove impurities and keep the fabric neutral, because the presence of impurities and acid and alkalinity will accelerate the decomposition of dyes under chlorine bleaching and non-chlorine bleaching conditions;

Use chlorine-resistant color fixatives to improve the chlorine resistance of dyes and strengthen the combination of dyes and fibers;

Chlorine bleaching color fixatives are about 1 level higher than the US standard requirements, and the Japanese standard requirements can reach level 4. It is mainly related to the different test methods and effective chlorine concentrations.

8. Color fastness of denim fabric to ozone

1) Factors affecting failure

Denim is generally dyed with indigo dye, which will decompose into indigo red under the action of strong oxidants, and ozone has a strong oxidizing effect.

Indigo red should be red, but the phenomenon seen in actual tests is more inclined to yellowing, which is related to the purity of the dye used, other chemicals added in the dyeing process, fabrics and finishing processes.

2) How to improve

Choose dyes with structures resistant to ozone oxidation

Antioxidant and anti-yellowing auxiliaries

Environmental protection projects

Formaldehyde problems

The sources of formaldehyde problems are very wide, such as color fixatives Y and M, some softeners, waterproofing agents, adhesives, stiffening resins, etc. Some of them will contain formaldehyde. At the same time, formaldehyde migration in the air will also cause formaldehyde to exceed the standard on the fabric, but these can be avoided, because with the improvement of environmental protection concepts, most dyeing and chemical auxiliaries have eliminated formaldehyde.

But now I will introduce two processes that cannot avoid formaldehyde problems.

One is that the auxiliary agent of the non-ironing finishing (resin finishing) will decompose formaldehyde during the shaping process, causing the formaldehyde content to exceed the standard.

The second is the permanent flame retardant process for cotton. There is also formaldehyde in the auxiliary agent, which will also cause a large amount of formaldehyde to exceed the standard. Last year, a company developed a permanent flame retardant process without formaldehyde for the first time in the world. It has not been widely promoted yet, and the process is not particularly mature.

At the same time, these processes also need to pay special attention to the formaldehyde problem: hard finishing, color fixation with formaldehyde, glue selection for flocking process, and even paint printing also need to select adhesives.

2. APEO exceeds the standard

APEO is strictly restricted by some countries, especially European countries, as a chemical indicator. Now let's take a look at how this substance gets on our fabrics. First, some of the scouring agents and penetrants used in the pre-treatment of our fabrics for dyeing, the detergents and leveling agents used in printing and dyeing, and the emulsifiers in the softener during post-finishing may be the source of APEO substances. Since a large number of TX and NP series surfactants were used as auxiliary raw materials in the past few years, it is difficult to prevent them. The only way is for printing and dyeing factories to insist on using environmentally friendly auxiliary agents and strictly prohibit the use of auxiliary agents containing APEO in the factory. Choosing the additives of Demei, Chuanhua listed companies or Rudolf Huntsman and Japan Nichika will be more secure

3. Heavy metal ions exceed the standard

Metal ions such as chromium and antimony are strictly tested in products exported to Europe. If they exceed the standard, they will have serious consequences like formaldehyde exceeding the standard. In the additives, there are fewer such metal ions, but some additives will cause exceeding the standard. For example, the flame retardant antimony trioxide emulsion contains a large amount of mercury. When the mordant dye is used in wool spinning, the mordant dye used is potassium dichromate or sodium dichromate or sodium chromate, Cr6+ will exceed the standard. The source of antimony is the grey cloth slurry, which is contained in the grey cloth itself. Some moisture absorption and perspiration additives

4. PCP (organic chlorine carrier) is an important mildew-proof preservative, which is easy to store. It is generally present in the leveling agent and repair agent used in dyeing. The carrier dye used for dyeing polyester-wool blends and polyester-optical blends may contain

5. Azo In the past, it was an important dye intermediate, existing in dyes. Now, most dye companies have excluded azo dyes. Occasionally, it exists in some unknown brand dyes. It is necessary to pay attention to wool yarn fibers (Yuyao area), which sometimes have azo exceeding the standard. It is recommended to test first and buy it back for production if it is qualified.

The above is an analysis of common problems that textile fabrics fail to pass the test and how to solve and improve them!