This will be the most comprehensive guide on the topic of color fastness, in this guide, you will learn the classification of the color fastness, and the way to test, improve and avoid the poor color fastness performance, and much more…
1.Color fastness definition: What is color fastness?
Another name for color fastness is dye fastness. It refers to the resistance of textile colors to effects such as color change or transfer during processing and use. The fastness grade, i.e., the degree of color fastness of fabric, is evaluated according to the discoloration of a sample and the staining of the undyed lining fabric.
During use, textiles are usually exposed to external factors such as light, washing, ironing, sweat, friction, and chemical agents. Some printed and dyed textiles are also subjected to special finishing processes, such as resin finishing, flame retardant finishing, sand-washing, and grinding. This demands that the color of printed and dyed textiles relatively maintain a specific fastness, i.e. good color fastness performance.
2. Harm of poor color fastness of textiles
The danger of a textile’s poor color fastness is quite eminent. When textile products with poor color fastness are exposed to water, sweat, sunlight or physical friction, the dyes may eventually fall off or fade. Thus, the appearance of the textile product is negatively affected. During use, the shed dye molecules or heavy metal ions may be absorbed by the human body through the skin, thereby endangering the user’s health, in short, poor color fastness is unacceptable.
3. Classification of color fastness, what are the different categories of color fastness?
In actual work, it is the end-use of a product and product standards that determine the test elements or conditions used. For example, the wool textile product standard stipulates that producers must test the wool’s color fastness to sunlight. Of course, the sweat color fastness of knitted underwear must be tested, while outdoor textiles (Such as parasols, light box cloth, canopy materials) must undergo a color fastness test to weather resistance.
There are six common color fastness classifications:
3.1. Color fastness to rubbing
Rubbing fastness refers to the degree of color fading of dyed fabrics after rubbing. This can either be from dry rubbing or wet rubbing. The rubbing fastness is determined from the degree of a prespecified white cloth’s staining, and it is graded in 5 levels. The larger the value, the better the rubbing fastness.
Lightfastness refers to the degree of discoloration of colored fabrics when exposed to sunlight. The Color Fastness to light test is done by comparing the degree of fade of the sample after simulating sunlight with a standard color sample divided into eight grades; 8, as the resulting value, implies the best while 1 implies the worst lightfastness. In essence, for fabrics to remain in optimal condition, they should not be exposed to sunlight for long periods, and they should also always be dried under shade, in a ventilated area.
3.3. Color Fastness to sublimation
This is the degree of sublimation dyed fabrics undergo in storage. The dye fastness of normal fabrics generally requires 3-4 grades in this category to meet wearing needs.
3.4. Washing Color Fastness
Washing or soaping fastness refers to the degree of the color change of dyed fabric after washing with a washing liquid. Usually, a gray graded sample card is used as the evaluation standard; that is, the color difference between the original sample and the faded sample is used for judgment.
Washing fastness is graded into five levels; grade 5 is the best while grade 1 is the worst level of washing fastness.
Fabrics with poor washing fastness should be dry-cleaned. But if they must be wet-washed, then other washing conditions may need to be tweaked and watched closely. For instance, the washing temperature should not be relatively high, and the washing time should be kept brief.
3.5. Color Fastness to perspiration
The Color Fastness to perspiration refers to the degree of color fading of a dyed fabric after small perspiration.
3.6. Ironing Color Fastness
This refers to the extent dyed fabrics may discolor or fade from ironing.
4. How to judge various kinds of Color Fastness and how to prepare for a Color Fastness test?
Seeing that Color Fastness is a relatively broad topic, founded on a hatful of professional knowledge, it is important to know some basic concepts and tools to help you understand as you read.
4.1 Color Fastness test terms
In printing and dyeing textiles under specific environmental factors, certain activities and reactions within the textile may result in color chroma, hue, and brightness changes. This effect is referred to as discoloration. Some of these occurrences within textiles include; when part of the dye is separated from the fiber, or the luminescent group of the dye is destroyed, or a new luminescent group is generated.
Staining is a phenomenon where part of the dye on a piece of fabric is separated from its originally attached fiber and transferred to other lining fabrics when placed under various environmental factors, thereby staining the lining fabric.
For garments composed of parts with different colors, dyes sometimes migrate from one area of the fabric to another, during storage and usually from dark parts to light parts. This phenomenon is different from sublimation because it is carried out at temperatures below sublimation temperature, and it also occurs with non-sublimation dyes. We can see this in the migration of dyes in polyester and other chemical fiber fabrics, as well as other raw materials.
The color transfer is mainly due to two reasons: the first is the transfer of dyes, especially the floating color of dispersing and reactive dyes. These dyes may migrate and be released from the fiber, dyeing the fiber on another sample’s surface. This usually happens with dark colors that dye light colors and stay on the other sample’s surface in a granular and embossed form. The second is that the fibers fall off under the action of friction and transfer from one sample to another.
4.2 Common grading tools for Color Fastness
The Color Fastness of textiles is graded by discoloration and staining gray cards. The gray cards currently in use include AATCC gray cards, ISO gray cards, JIS gray cards and national standard GB gray cards. These gray cards are only slightly different in the grayscale.
The Color Fastness rating gray card is a card characterized by a specific gradient increase or decreases. A color-changing gray card comprises one group of standard gray levels and another group of color-changing gray levels. The original gray levels remain unchanged throughout a test, while the second group of color-changing gray levels decreases gradually to form a discoloration contrast between the two.
Color changing gray card
This contrast card comprises one standard scale of gray and a decreasing scale of gray chroma.
The grayscale rating for the color change is determined using 5-grade levels and nine grades system with grade 5 representing the best Color Fastness and grade 1 representing the worst Color Fastness. The middle levels can be assessed as half grade: grade 4-5, grade 4, and grade 3-4.
Stained gray card
This comprises of a standard scale of white with a corresponding group of increasing gray chroma. There are five grades and nine grades system; grade 5 implies virtually no staining occurred. Hence great Color Fastness while grade 1 signifies the worst Color Fastness, and the middle can be assessed as half grade, such as grade 4-5, grade 4, and grade 3-4.
It can be seen from the above data that the so-called gradient decreasing method appears in the form of 1:2:4:8:16. The gray card looks at the gradient level of the color change, so you must observe the gradient level of this change when grading so that there will be no such incident as only evaluating gray and black, but no other colors.
4.3 How to use the Color Fastness gray card correctly
[Cover sample card]
(As shown in the figure above) The masking card is used in grading. Each hole is used for multi-fiber cloth staining evaluation, rubbing fastness staining evaluation and general staining evaluation (self-staining color evaluation, single fiber Cloth stain evaluation).
The use of masking cards is more conducive to focus on the samples that need to be graded while covering other areas to prevent other colors from affecting the vision.
When grading, the masking card needs to be linked
4.4 Environmental requirements for Color Fastness ratings
【Light source and equipment】
The preferred general light source is the D65 light source. Its service life tube is 2000 hours. Customers can also specify other light sources, such as the F light source, 84-P light source, UV light source, etc.
The rating process should be done in a darkroom of constant humidity and constant room temperature. The color of the darkroom wall and the objects on the wall should be painted in neutral gray as well, which is similar to the rating gray card between level 1 and level 2 (approximately Monsell color Card N5). As shown in the picture above, the left is a neutral gray wall when the lights are turned on, and the picture on the right shows when the lights are turned off. It is required that the entire darkroom must not have any other light sources except the light source of the rating lightbox. Also, ensure that no other sundries appear on the rating platform.
【Rating angle 】
To use the gray card to rate the samples, you need to use the correct rating angle. The standard generally used entails that the sample and the horizontal plane be at 45° while the light source for rating and the sample are kept at 45°. The grader’s eyes are meant to be at 90° to the sample while the distance between the eyes and the sample should be 50-70cm.
- The grader should not be color-blind. They can be tested using a color-blindness detection chart or Farnsworth-Munsell 100 hue test kit.
- Clothing requirements: Gray clothes are best. Avoid bright-colored clothes, bright-colored nail polish, and any items that may reflect the light source.
- Do not wear colored glasses.
- Do not rate when tired or sick. Rating is a subjective activity, and mood will affect the psychological, subjective judgment of color; for the same sample, when one is happy, it is one result. When they are down, it is another result.
- Observers must adapt to standard lighting conditions for at least 2 minutes before observation commences. This is to let the eyes adapt to the current light source environment.
- The raters require strict training and must pass the preset assessment.
It is necessary for different personnel to carry out eye calibration on the same sample periodically to ensure that the error between personnel is minimized. It is also necessary to carry out eye calibration between laboratories occasionally.
The grading work displays the results of Color Fastness testing and is the last process of the Color Fastness testing task. No matter how accurate and standardized the previous processes are, there will be errors in the grading, and all the efforts of the former could be in vain. As far as current Color Fastness testing is concerned, grading has always been a difficult task to manage. On a small scale, it is necessary to ensure the consistency of all personnel’s eyes in the laboratory. On a large scale, it is necessary to ensure the consistency of the eyes between the testing institutions. Since each brand cooperates with many laboratories, the consistency of eyesight between laboratories is particularly important.
5. Detailed explanation of various Color Fastness tests
5.1 Color Fastness to rubbing test
Color Fastness to rubbing is a type of textile Color Fastness inspection, and it is generally one of the most common inspection types in the textile trade. It refers to the ability of the color of textiles to resist friction, and that is both dry friction and wet friction.
5.1.1 Test template of Color Fastness to rubbing
The model generally followed to test for Color Fastness to rubbing textiles to fix the specified size textile sample on a friction tester platform with a clamping device. Then, rub it with a dry friction cloth and a wet friction cloth, respectively. In the end, the degree of staining of white cloth is used as the evaluation basis, and it is graded against a set of standard Color Fastness to staining gray scales.
The gray sample card used to determine the fastness rating is divided into five grades; the higher the grade, the better the rubbing fastness. A fabric with poor rubbing fastness could rub off dyes on basically anything, and that is undesirable for end-users.
5.1.2 Dry friction test
Put a piece of (50×50) mm rubbing cloth (standard white cotton cloth) on the rubbing head under standard atmosphere (temperature 20℃±2℃, humidity 65%±4%), humidity control for more than 4 hours. Make sure the direction of the friction cloth is consistent with the movement direction of the friction head. Adjust the running speed of the rubbing head to one reciprocating friction cycle per second, ten times, which amounts to a total of 10 cycles of friction. The friction stroke or reciprocating movement on the sample should be (104±3) mm, and the applied direction is vertically downward. This downward force should be (9±0.2) N. After the entire ten cycles are completed, remove the friction cloth, adjust the humidity (over 4 hours), and remove any excess fibers on the friction cloth that may affect the rating. As shown:
5.1.3 Wet friction test
Immerse the weighed piece of friction cloth completely in distilled water, take it out, and reweigh the friction cloth to ensure that the moisture content of the friction cloth reaches 95%-100%. Then apply the same operating method as in the dry friction test.
5.1.4 Textile rub resistance test rating
After performing the above test process, we need to take the moistened friction cloth to the grading room and place it in the standard light source box, then use the gray sample card to evaluate the staining grade of the friction cloth.
Place three layers of friction cloth on the back) as shown in the figure:
5.1.5 Comparison of common standards of textile Color Fastness to rubbing
The commonly used standards for Color Fastness to rubbing are GB/T 3920-2008, AATCC 8-2007, AATCC 116-2010 and JIS L 0849-2004. We can analyze the similarities and differences between these four standards through the following table.
It can be seen from this table that different testing standards have different requirements depending on the size of the sample cloth. When the customer prepares the sample cloth, if the tested sample is a fabric or carpet: prepare two sets of samples with a size not less than 50 mm × 140 mm and group two pieces of each set. (When sampling, one piece of fabric is parallel to the warp yarn, and the other piece of fabric is parallel to the weft yarn.) Another sampling method is to sample at a certain angle from the sample’s length to the warp and weft of the fabric.
If it is a pile fabric and the pile is easy to distinguish, the pile’s direction when cutting the sample should be consistent with the length of the fabric. Under normal circumstances, the national standard and the European standard adopt the method of taking one piece in each of the latitude and longitude directions. In contrast, the American standard adopts the method of sampling with an inclination to 45 degrees.
If the tested fabric is the yarn: it needs to be woven into a fabric with a sample that is not less than 50 mm × 140mm. Alternatively, the yarn can be wound parallel to a cardboard of the same size as the sample and along the length of the cardboard.
5.1.6 Analysis of factors affecting Color Fastness to rubbing
- The influence of fabric surface morphology
Under dry conditions, it is very easy to perform dry rubbing on a rough surface or sanded and raised fabrics, such as hemp fabrics, denim fabrics and pigment printing fabrics, because unfixed dyes are the main cause of poor Color Fastness to rubbing. This is because the dye, paint, or other colored substances accumulated on the fabric’s surface are ground down. Some colored fibers are even broken while colored particles are formed, which further reduces the Color Fastness to dry rubbing. For sanded or raised fabrics, the fluff on the surface of the fabric and the surface of the friction cloth are at a certain included angle, which is not parallel, so that the friction resistance of the friction head during reciprocating motion increases, making this kind of fabric resistant to drying. Hence, the Color Fastness of rubbing would decrease.
- The influence of fabric structure
The surface of a sample of light and thin fabric (usually synthetic fiber or silk fabric), due to the relatively loose fabric structure, during dry friction, the sample will slip with the movement of the friction head under the action of pressure and friction. The slippage partially increases the frictional resistance and improves friction efficiency as well. But in wet friction with these chemical fibers, the reaction is different from the reaction with cellulose fibers.
Due to the extremely low moisture absorption of the fiber or the insignificant water puffing effect, and the presence of water as a lubricant, the Color Fastness to wet rubbing of such light and thin fabrics is significantly better than their Color Fastness to dry rubbing.
Therefore, it is not uncommon for certain fabrics to have better Color Fastness to wet rubbing than dry rubbing. In these cases, the selected dye types, dye performance, dyeing, finishing process conditions etc. will also affect the Color Fastness to rubbing. But when their influence is compared with the influence of physical factors such as the texture and surface morphology of the fabric, they seem quite unimportant.
However, studies revealed that this effect usually pertains to products with dark colors, such as black, red and navy blue. Of course, due to the dyes, printing and dyeing processes of corduroy, twill and other pigment printing fabrics, under wet conditions, usually have a Color Fastness to wet rubbing grade of level 2, or lower and this is not superior to their fastness to dry rubbing.
- The influence of reactive dye chemical structure
When a cellulose fiber fabric dyed with reactive dyes is subjected to the wet rubbing fastness test, two main factors could cause color transfer: the water-soluble dye is transferred to the rubbing fabric during rubbing, causing the original color to fade, therefore staining the rubbing cloth. The second is that some of the dyed fibers break during rubbing, forming tiny colored fiber particles that are transferred to the rubbing fabric, which, of course, stains it.
Factors that may affect the Color Fastness of reactive dyes to wet rubbing include the structure and characteristics of the reactive dyes themselves, the fabric’s properties, the effect of pretreatment, cloth surface damage, surface finish, etc. Furthermore, the dyeing process and the effect of soaping after dyeing the fabric, the effect of fixing treatment, and the effect of dyeing fabric finishing can all contribute to influencing the Color Fastness of reactive dyes.
Studies show that the covalent bond strength, bond stability and adhesion formed by reactive dyes of varying chemical structure on cellulose fibers are different. On the other hand, there is no significant difference in the effect of the Color Fastness to wet rubbing of dyed fabrics. When the dyed fabric is wet rubbed, the covalent bond formed between the dye and the fiber will not break; hence, floating colors won’t be produced. The transferred dyes are usually supersaturated dyes that do not form a covalent bond with the fiber and only rely on van der Waals forces to produce adsorption, and these are the so-called floating color.
- Influence of reactive dyeing degree
The Color Fastness to wet rubbing of reactive dye-dyed fabrics is closely related to the depth of dyeing in the sense that, when wet rubbing, the amount of color transfer and the depth of dyeing are almost in a good linear relationship. Excessive dyes cannot be combined entirely with fibers. They will only accumulate on the fabric’s surface to form floating colors, which seriously affects the Color Fastness to wet rubbing of the fabric.
Cotton fibers without special treatment and under wet conditions, will swell, increase friction, and decrease fiber strength. These create favorable conditions for the breakage, shedding and transfer of color in colored fibers. Therefore, we can improve the fabric’s surface finish and hair effect through pretreatment of the cellulose fiber before dyeing. Some of these pretreatment processes include; mercerizing, singeing, cellulase finishing, scouring, bleaching, washing, and drying. This will reduce friction resistance and reduce floating color, thereby effectively improving the Color Fastness to wet rubbing of the fabric.
- The effect of softener
We can improve the Color Fastness of reactive dye printing through soft finishing. Softeners have a lubricating effect when applied to the fabric and can reduce the coefficient of friction to prevent the dye from falling off. Cationic softeners can also form lakes with anionic dyes, and the dyes won’t easily fall off. Simultaneously, the formation of the color lake eventually reduces the dye’s solubility and improves the wet rubbing fastness. However, softeners with hydrophilic groups will most likely deter the improvement of Color Fastness. In the production practice process, the dye’s water-soluble group can be blocked using a fixing agent. With this, the pH value of the finished colored cloth’s fabric surface can be controlled, floating color can be removed, smoothness of the fabric can be improved, and the wet rubbing fastness of the fabric can also be improved. Proper pre-bake at the front stage can avoid dye “migration.”
During pretreatment, the factors and properties that require the most attention are the amount of alkali, steaming time, washing method, sufficient soaping, etc. The first two are closely related to the degree of hydrolysis of the dye, and the latter two are directly related to the dye’s floating color.
The dyed fabric, especially the long-car pad dyeing, must undergo sufficient washing, soaping, and other processes to remove the floating color and the unreacted and hydrolyzed dyes on the fiber surface. This will avoid undesirable effects on the fabric’s Color Fastness, but it will result in poor Color Fastness, and the shade will be darker when not paid the necessary attention.
Among the factors mentioned above affecting the Color Fastness of fabrics to rubbing, their respective principle of action and the degree of influence is very different. The Color Fastness problem seems simple, but the factors involved are quite complicated. Over the years, whether in dye research and production or textile dyeing and finishing, people have invested a lot of manpower and material resources to solve the problem of Color Fastness in textile products. Thankfully great progress has been made. Although dyestuffs, new processes and new additives continue to emerge, there are still many problems that need resolving.
5.2 Textile Lightfastness test
The lightfastness of textiles has been paid progressively more attention at home and abroad. Presently, China’s textile industry product standards (especially the new standards endorsed in recent years, excluding underwear standards) all use lightfastness as one of the assessment standards. For example, the silk product standards publicized by China before did not stipulate the assessment of lightfastness. Still, the promulgated standards have now taken the lightfastness of elastic silk as the assessment index. With chemical fiber like silk fabric and cotton product standards, lightfastness is also taken as an important evaluation index, and some product standards even take lightfastness as an evaluation index.
5.2.1 Comparison of common test methods and standards for lightfastness
There are many test methods for lightfastness. The following table lists several commonly used standard methods.
5.2.2 China’s current effective lightfastness test method standard
- -Color Fastness to light: This is done by exposure to sunlight under the specified conditions and not exposed to rain. The Color Fastness to light of the sample in question is then evaluated with reference to the blue wool standard.
- -Color Fastness to artificial light: Xenon arc testing refers to the exposure of a sample to an artificial light source equivalent to sunlight under specified conditions. The Color Fastness to light of the sample is then evaluated with reference to the blue wool standard.
- -Color Fastness to weather: This means outdoor exposure of a sample without any protection and under specified conditions. The sample is then compared with the blue wool standard to evaluate its Color Fastness.
- -Color Fastness to human-made weather: This refers to using xenon arc to spray exposure in a xenon lamp tester under specified conditions. The exposed sample is then compared with the blue wool standard to evaluate the Color Fastness.
- -Composite Color Fastness to light and perspiration: Expose the sweat-treated sample in the instrument, and then evaluate its Color Fastness to light and perspiration to determine its sensitivity. Among them, the xenon arc in the Color Fastness to artificial light is the most used standard. Most textiles in China are tested according to this standard method when assessing the Color Fastness to light.
5.2.3 The relevant standards of the American lightfastness tester
Color Fastness to light is suitable for indoor textiles. Weather resistance of fabric (through xenon arc) is suitable for outdoor textiles. Among them, lightfastness is a widely used textile light resistance and stability standard.
Its main measuring range:
- Lightfastness test of dyes: lightfastness test of dye is measured under light (wavelength 380nm～750nm) and certain temperature and humidity conditions.
- Weather fastness test of dyes: under the combined influence of light (wavelength 380nm～750nm) and a certain temperature, humidity and rain, the weather-fastness of dyes is measured.
- Weather fastness test of textiles: Under the combined action of light (wavelength: visible light = 380nm～750nm; ultraviolet light = 300nm～380nm) and climatic conditions, the weather-fastness of textiles is measured.
5.2.4 The best way to test lightfastness
The fabric’s reaction to light happens to be one of the most important test aspects in all Color Fastness tests. Of course, for manufacturers, the performance of fabrics in washing, dry cleaning, rubbing, sweat absorption, and exposure to different solutions is crucial information. However, because fabrics are sensitive to light and their reactions to light are difficult to predict, accurate and reliable testing is critical.
For many manufacturers, lightfastness testing is an important part of R&D and quality control. However, it is also one of the most difficult tests to become proficient at. This is because most materials take months or even years to respond under sunlight. It is not feasible to test the fabric under natural light in an actual application environment. What’s more, we can’t say many R&D departments are willing to wait patiently.
Many manufacturers choose laboratories for testing. They simulate natural light to speed up the test process. The most successful technique used is the xenon long arc radiation method. This singular reliable method of simulating and reconstructing the natural light spectrum uses various filters to reproduce special optical conditions.
The lightfastness test is not as simple as placing the fabric under a specific light source to observe its reaction. Temperature and humidity must also be considered because both temperature and humidity influence the fabric’s response to light more so. Therefore, the lightfastness tester must control these environmental factors, that is, create corresponding environmental conditions for each test, and keep them constant throughout the process.
Also, if a certain fabric is used outdoors, the simulation of weather factors, especially rain, is another issue that must be considered. Therefore, the equipment must include a water sprinkler system that simulates rainy days and simulates climate conditions in different parts of the world.
5.2.5 How to improve the lightfastness of textiles? Three reliable methods
The light-fading mechanism of dyes is very complicated. But simply put, it is due to the dyes being excited after absorbing photons, and the occurrence of a series of photochemical reactions to destroy the fundamental dye structure, which ultimately leads to discoloration and fading. The lightfastness of textiles mainly depends on the chemical structure of the dye and its aggregation state, combination state and mixed color matching. Therefore, selecting dyes rationally is very important.
- Choose dyes according to fiber properties and textile applications. For cellulose fiber textiles, it is advisable to select dyes with good oxidation resistance; for protein fibers, it’s best to select dyes with good reduction resistance or containing weak oxidizing additives. And for other fibers, dyes should be selected based on their effect on fading. Enhancing the azo group’s photooxidation resistance in the dye molecular structure can be achieved during the dye synthesis process. Some strong electron-withdrawing groups are usually introduced at the azo group’s ortho position, which would reduce the electron cloud density of the azo nitrogen atom. Also, it is possible to introduce hydroxyl groups at the two ortho positions of the azo group and use its coordination ability to form complex structures with heavy metals, thereby reducing the electron cloud density of the azo group hydrogen atoms, shielding the azo group, and ultimately improving the dye Fastness to light.
- Dyes should be selected according to the color depth.Many experiments have proved that the lightfastness of reactive dyes on cellulose fibers is directly proportional to the depth of the dyed luster, that is, the darker the color, the better the lightfastness. This is because the higher the concentration of the dye on the fiber, the greater the degree of aggregation of dye molecules, the smaller the surface area of
the same amount of dye in contact with air, moisture and light, and ultimately, the lower the probability of the dye being oxidized by light. On the contrary, when the colors are lighter, the dyes are mostly in a highly dispersed state on the fiber. The probability of exposure to light is higher, which will eventually reduce the Color Fastness to light. Therefore, for dyeing light-colored varieties, dyes with higher lightfastness should be used. Besides, many finishing agents such as softeners and anti-wrinkle finishing agents are added to the fabric, which will also reduce the product’s lightfastness. Therefore, dyes that are not sensitive to these finishing agents should be selected.
- Dyes with good light resistance stability and compatibility should be used for color matching. The fading properties and light fading mechanisms of various dyes are different. Sometimes, the presence of one dye sensitizes the fading of another dye. When matching colors, dyes that do not sensitize each other and can even improve light resistance’s stability should be used. This is especially important when dyeing dark varieties such as black. One of the three primary colors fades too fast, and this will quickly cause the dyed fiber or fabric to change color. The faded dye residue will also affect the light stability of the other two dyes that are not faded. To obtain higher lightfastness, it is expedient to apply reasonable control of the dyeing process, fully combining the dye and fiber, and avoid hydrolyzed dyes and unfixed dyes lingering on the fiber as much as possible.
5.2.6 FAQs On Lightfastness Test
The lightfastness tester in textile testing equipment is relatively conventional, but it is also one of the most important Color Fastness test items.
The lightfastness test project is not difficult to carry out, but various problems are often encountered in the actual operation process. Here, we analyze common problems in the national standard, ISO and AATCC lightfastness test standards for your reference.
Q1. What is the difference between blue wool cloth 1-8 and L2-L9? Can they replace each other?
In GB/T 8427 and ISO 105 B02, blue wool standard samples, 1-8 and L2-L9, are described in detail. They are all wool and have eight levels of blue labels, and each higher numbered blue label target or reference has lightfastness that is about one time higher than the previous number. But different dyes and manufacturing processes are used.
Blue labels 1-8 are dyed with eight dyes of different lightfastnesses, and this is suitable for European exposure conditions specified in GB/T8427 and ISO105 B02. For L2-L9, the fibrils are dyed with two dyes, and then the two dyed fibers are made into blue label L2-L9 in different proportions. This fits the US exposure conditions specified in GB/T8427 and ISO 105 B02. And it is suitable for AATCC TM 16. Nonetheless, the blue labels 1-8 and L2-L9 cannot be mixed, and the test results cannot be interchanged.
Q2. The lightfastness tester has relative humidity in the cabinet. Why do we need to calibrate it with humidity control standards?
At present, most lightfastness testers can display the relative humidity in the cabinet. Still, GB/T 8427 and ISO 105 B02 stipulate that the cabinet’s humidity should be calibrated with humidity control standard samples every day. The reason is that the standard sample calibration of the humidity control cloth is not the “relative humidity” in the cabinet, but the “effective humidity.” Effective humidity is also called absolute humidity. It is defined by combining air temperature, sample surface temperature, and relative air humidity that determines the moisture content on the sample surface during exposure. “Effective humidity” directly affects the test results of the lightfastness of humidity-sensitive samples. Therefore, the GB and ISO standards stipulate to check the humidity in the cabinet every day.
The humidity control standard is cotton fabric dyed with red azo dye. The method of use is as follows:
- Put a piece of humidity control cloth (not less than 45×10mm) together with the blue wool standard sample on the hard cardboard and place it in the middle of the sample holder as much as possible.
- Expose the partially covered humidity control standard sample and the blue wool standard sample at the same time until the color difference between the exposed and unexposed parts of the humidity control standard sample reaches level 4 of the color change sample card.
- At this time, the blue wool standard sample is used to evaluate the color change of the humidity control cloth and which blue wool standard sample is consistent. The color difference should be the same as that of grade 5 blue wool cloth. If it is inconsistent, you need to re-adjust the controller to maintain the specified blackboard temperature and humidity.
Q3. What is the role of the xenon reference fabric in AATCC TM 16?
Xenon Reference Fabric is a purple polyester fabric. Its function is to determine whether the temperature in the box is correct. The used method is to place the xenon reference fabric on the sample holder for continuous exposure for 20±2h. If the xenon reference fabric’s color change is consistent with the xenon reference standard sample or the color difference is 20±1.7 CIELAB units by measuring the color with the instrument, the proof box body temperature is normal.
Q4. In some product standards, some lightfastness requirements require method 3, and the quality requirements are intermediate levels, such as 3-4. How should we test it?
Certain product standards do have such a requirement, and some experts say that this formulation is completely wrong because experimenters cannot choose the blue wool standard. However, because some current product standards are stipulated in this way, it is recommended for operators to use Method 3 for experiments, and then refer to Method 1 for evaluation. For example, if the standard requirement is 3-4, we choose the 4th and 3rd blue wool standard to use the requirement experiment specified in Method 3. When grading, you can refer to the method one grading method because there are 4 and 3 blue wool Standard samples. Theoretically, we can judge whether the test result of the sample reaches 3-4 levels.
Q5. What is the unit of AFU in the American AATCC standard? What is the relationship with the number of hours?
AFU is an energy unit, and it is the acronym for the “AATCC Fading Unit.” It is defined as 1/20 of the exposure energy required to make the L4 blue wool standard fade to level 4 of the color-changing gray card. This means 20 AFU of energy is needed to make the L4 blue wool standard fade to level 4 color change. The AFU and radiant energy values
The relationship between AFU and hours can be calculated by a formula, assuming that when the xenon arc lamp is operated under 1.10W/m2•nm conditions, the energy required to make L4 reach level 4 color change is 85 kJ/m2.
85 kJ/m2=1.10 W/m2 x 3.6 x (hours)
Hours = (85 kJ/m2) / (1.10W/m2x3.6) = 21.5
This shows that when the radiant energy of the xenon lamp changes, the number of hours from the day to the specified AFU will also change. Only when the lamp is operated at 1.10 W/m2•nm can the energy of 20 AFU be reached in 21.5 hours.
5.3 Color Fastness to washing
Washing is one of the most common cleaning and maintenance methods for clothes. The Color Fastness to washing determines the color firmness of textiles in different detergents and different washing environments. There are many ways to test Color Fastness to washing. The general principle is to imitate the state of household or commercial washing. Under the specified time and temperature conditions, after stirring, rinsing, and drying, use a gray sample card or instrument to compare the original sample to evaluate the color change of the sample and the lining fabric’s staining. Various methods may have certain differences in temperature, test solution, washing procedures, drying procedures and a decision to add steel balls or not.
5.3.1 Comparison of common textile Color Fastness standards:
Chinese standard: GB/T 3921-2008; GB/T12490-2007
International standards: ISO 105C10:2006; ISO105C06:2010
EU standards: EN ISO 105C10:2007; ENISO 105C06:2010
British Standard: BS EN ISO 105C10:2007; BSEN ISO 105C06:2010
American Standard: AATCC 61-2010
Australian Standard: AS 2001.4.15-2006
German standard: DIN EN ISO 105C10:2007; DINEN ISO 105C06:2010
Japanese Standard: JIS L 0844:2011
Take GB/T 3921-2008 “Textile Color Fastness test Color Fastness to soap” as an example to introduce you.
5.3.2 Test process of Color Fastness to soap and washing:
(1) Sample: Take a 100mm×40mm sample with the front side in contact with a 100mm×40mm multi-fiber lining fabric, stitched along a short side to form a combined sample. Or take a 100mm×40mm sample, sandwich it between two 100mm×40mm single fiber lining fabrics, and stitch along a short side to form a combined sample.
(2) Preparation of test solution: 5 grams of soap per liter of tertiary water is used for tests A and B, and 5 grams of soap and 2 grams of sodium carbonate per liter of tertiary water are used tests C, D and E, respectively.
(3) Test: Put the combined sample and the specified number of steel balls in the container, according to the standard test conditions. Then inject the required amount of soap solution preheated to the test temperature ±2℃, so that the bath ratio is 50:1. Close the container, adjust the temperature and time according to the standard and start the machine. Remember to start timing when the container is closed.
(4) Washing and drying: For all tests, take out the combined samples after washing, wash them twice in tertiary water, and then wash them in running water until they are clean. Squeeze the excess water from the combined sample by hand, flatten the sample between two unused filter papers to remove the excess water, and then hang it to dry in the air of temperature not exceeding 60℃. The sample is only connected at the position of the suture.
(5) Grading: Use the gray sample card or the instrument to compare the original sample to evaluate the sample’s discoloration and the staining of the lining fabric.
(6) Result report
5.3.3 Analysis of the reasons for the unqualified test of Color Fastness to the washing of textile fabrics
- The fabric structure, fiber composition and corresponding dyeing process conditions are the primary factors that affect its Color Fastness to washing.Generally, the Color Fastness of single-component fabrics is better than that of blended fabrics. All polyester, cotton, nylon and all wool fabrics are less likely to have color problems. The dyes corresponding to the fabric components are selected. After processing by the dyeing factory, they can usually achieve 3-4 grades or more. Cleaning and curing the color and other processes are properly controlled, and level 4 can be easily achieved.
For blended fabrics, the Color Fastness to washing after dyeing is generally lower than that of the corresponding single-component fabrics, especially when the dyeing process is improperly controlled. For example, when a polyester-spandex blended fabric is dyed in dark colors such as black and red, the Color Fastness to washing often fails.
Using disperse dyes (A class of non-soluble, nonionic dyes that depend on dispersing agents to spread color in synthetic fabrics) to dye polyester fibers generally stains spandex seriously. When selecting disperse dyes, it is necessary to consider whether they have good dyeing properties, and at the same time, to ensure that the staining on spandex is relatively easy to remove.
Some dyeing factories in Xiaoshao, in a one-sided pursuit of output, often use high temperatures to quickly shape the finished product. But when the temperature is too high, the dye molecules will easily escape from the polyester molecular structure. Various surfactants on the fiber surface accelerate this process, resulting in the floating color’s appearance on the surface of the finished product. For polyester, nylon, acetate, and spandex dyeing with disperse dyes, the thermal migration phenomenon is an important reason for these fabrics’ unsatisfactory Color Fastness and the heavy staining of acetate lining and nylon lining in six-fiber staining. The thermal migration of disperse dyes makes the dyes that have penetrated into the fiber to migrate to the fiber’s surface and accumulate on the surface of the fiber. The deeper the dyeing depth and the higher the post-setting temperature, the more obvious the above phenomenon is. After dyeing, it is important to reduce cleaning treatment to remove the disperse dyes contaminated by the spandex component and the floating color on the polyester surface. At present, acid reduction cleaning with thiourea dioxide or alkaline reduction cleaning with sodium hydroxide and soda ash can improve the washing fastness of polyester-spandex blended fabrics to above level 4, which should meet the requirements of high-end brand clothing.
In the actual production and life process, nylon, silk and wool blended fabrics often encounter poor washing fastness. Nylon is similar to protein fibers such as silk and wool. It contains a certain amount of amino and carboxyl groups in its molecular structure, so acid dyes are generally used for dyeing. As a water-soluble dye, the acid dye has a small molecular volume, which makes the result of a wet treatment fastness test on fibers dyed with acid dye poor, especially its Color Fastness to washing. The dissolution of the dye is relative to the water solubility of the dye molecule. The sulfonic acid group in the dye binds to the fiber by hydrogen bonding. When the dyed fabric is immersed in water, the hydrogen bond is cut off, and part of the swollen dye will leave the fiber and dissolve in water. When the dyed material is stirred in the washing machine, the pigment of insoluble dye will fall off from the fiber due to the stirring. The higher the washing temperature, the larger the bath ratio, the longer the time, the more intense the stirring, and the more the dye falls off. In addition, the presence of surfactants in the washing process will greatly increase the dissolution of the dye from the fiber. The main reason for dye removal is that the pigment molecules have lipophilicity, which can co-dissolve with the surfactant’s hydrophobic base, thereby pulling the dye away from the fiber. To increase the washing fastness of acid dyes, we must first choose dyes with larger dye matrix and relatively few water-soluble groups to limit the dye’s mechanical movement inside the fiber and try to increase the bond between the dye matrix and the fiber strength. Furthermore, the tannin method and synthetic fixative method can be used, and after dyeing, the fabric is fixed.
- Using different test methods, the same test method, and different links of the operating methods also have an important impact on the test results of Color Fastness to washing. At present, domestic and foreign textiles have endorsed and implemented standards for the Color Fastness to washing. These standards have been revised and improved many times, including the European standard ISO 105 C10:2006, the national standard GB/T 3921-2008, and the American standard AATCC 61:2013. However, the test method is basically the same as in the test principle, but the test conditions are different. The common washing condition parameters are shown in Table 1.
It can be seen from Table 1 that the test conditions of the European standard and the national standard are the same. In contrast, the American standard differs greatly from the European standard and the national standard in whether steel balls are added, the detergent used, and the washing time, all of which ultimately lead to different test results. In the early stage of testing, two sets of knitted fabric samples of dark coffee and dark wine red, as well as two sets of woven fabric samples of blue denim and white and black striped woven fabric were used. Furthermore, the European standard, the national standard and the American standard were used respectively. The same lining conditions were tested, then the Color Fastness to the washing of the test sample was determined. The test results showed that the test results of the national standard and the European standard have a small difference, but there is a big difference between the two and the American standard. In terms of color change, the color change of both the national standard and the European standard is lighter, and both are generally 0.5 grade higher than the American standard. In terms of staining, the national standard and the standard European colors are heavier, and their staining grades are generally 0.5 lower than that of the standard American level.
The Color Fastness test for washing in the laboratory includes multiple procedures: sampling, lining, washing test, drying, grading. Even if it is the same test method and the same test parameters, different inspectors are subject to their habits, subjective judgments and other human factors. The impact of the test results will also lead to certain differences in the test results, so each link must be operated in strict accordance with the standard and unified specifications. Otherwise, it will affect the Color Fastness rating results to a certain extent.
- The influence of sampling on the test results of Color Fastness to washing: According to GB/T 3921-2008, when the sample is fabric, the sampling size is 40mm×100mm. However, many types of daily test samples in the laboratory are divided into plain, yarn-dyed, printed, and dyed fabrics. The correct extraction of representative samples will have a greater impact on the test results within the specified size. The dark and light gradual dyeing samples have a natural transition from multiple colors and gradually change colors from dark to light or from light to dark. When sampling, avoid the position where the color is gradual and cut two test samples at the evenly dyed light and dark positions. If the color of the sampling location is not uniform, it will easily affect the test results and is not representative.
- The influence of the selection of multi-fiber standard lining fabrics on the test results of washing fastness: In the GB/T 3921-2008 standard, the choice of lining fabrics can be two single-fiber lining fabrics or more fiber lining fabric, but the last test is more convenient. The multi-fiber interlining fabrics include DW type (multi-fiber interlining fabric containing wool and acetate) and TV type (multi-fiber interlining fabric without wool and acetate). In selecting multi-fiber lining fabrics, the national standard GB/T 7568.7-2008 “Textile Color Fastness test standard for lining fabrics Part 7: Multi-fiber” general requirements stipulate that: some Color Fastness tests cannot use wool and acetate. Also, when using fiber, TV type should be used instead of DW type. However, the expression of “certain Color Fastness tests” is rather vague. The national standard GB/T 3921-2008 does not specify the test conditions, which will lead to the use of different multi-fiber standard lining fabrics, and the results obtained will be different. Randomly select 23 woven fabrics of different colors and various fiber components as samples. According to method C(3) of the national standard GB/T 3921-2008, cut two samples from each of them, and compare them with DW type and TV type multi-fiber. Stitch the standard lining into a combined sample for testing, and the test results show that most samples use DW-type multi-fiber standard lining fabrics more than the TV-type test. The results are lower, while the same fiber strips of acrylic and the staining grade of polyester, nylon and cotton, DW type is 0.5 to 1 grade lower than TV type.
- The influence of different grading methods on the test results of Color Fastness to washing: The Color Fastness can be graded by eye or instrument. A neutral gray background is required for eye grading, the lighting conditions of sunny day and daylight (9:00-15:00), or an equivalent light source with an illuminance of 600lx and above. The incident light should form an angle of about 45˚ with the textile surface. The optimal observation direction is perpendicular to the surface of the textile. Furthermore, the color of the cover plate covering the original sample and the sample after the test should be the same while the size and shape should be similar. The grader must wear neutral gray overalls, and the environmental color influence should be avoided during the grading process. At the same time, the grader must have a clear understanding of the relevant standards, be familiar with the standard requirements and the enterprise’s relevant regulations, and correctly assess the grade of the combined sample. However, due to the differences in gaze between different raters, the rating results will be affected significantly. Therefore, it is necessary to compare the gaze differences within the specified time. This is how some human errors can cause unnecessary losses to enterprises and customers.
Under normal circumstances, for all kinds of fabrics with poor Color Fastness to washing, washing and fixing can effectively prevent the unfixed dyes from fading. Generally, the floating color remaining in the fiber pores and on the surface greatly influences the Color Fastness to wash. A good washing process and corresponding cleaning agents can fully remove the unfixed dyes. For fabrics dyed with direct, reactive, and acid dyes, after the fabric is cleaned, the corresponding reactive fixation and acid fixation processes can effectively improve the fabric’s Color Fastness. NB Fixation can be derived by dividing the mass of dye absorbed in the fabric or yarn by the original mass of dye in the water bath.
5.3.4 Summary of sampling methods for Color Fastness to washing:
Large-scale testing institutions adopt a process-based work method for Color Fastness testing, usually divided into sampling posts, test posts, and rating posts. Therefore, even if it is the same test method, different inspectors are affected by habit and subjective judgment in sampling methods, causing certain differences in test results.
The sampling of Color Fastness to washing must first consider the problem of lining fabric. Taking GB/T 3921-2008 as an example, this standard specifies that the choice of lining fabric can be a multi-fiber lining fabric or two single-fiber lining fabrics.
The multi-fiber lining fabrics include:
(1) Multi-fiber lining fabrics containing wool and cellulose acetate (used for tests at 40°C and 50°C, and in some cases can also be used for tests at 60°C, but needs to be indicated in the test report).
(2) Multi-fiber lining fabrics without wool and acetate (used for some 60°C tests and all 95°C tests). Single-fiber lining fabrics include cotton, wool, viscose, polyamide (nylon), polyester (polyester), polyacrylonitrile (acrylic), ramie, silk, and acetate.
Taking the multi-fiber lining fabric test as an example, the sampling methods of different types of samples in the washing fastness test are analyzed in detail.
The laboratory’s daily test samples are roughly divided into plain samples, yarn-dyed samples, printing samples, dark and light gradient dyeing samples, embroidery and car pattern samples, sequins, hot diamond samples, yarns and loose fibers, hollow fabrics, etc. When GB/T 3921-2008 requires the sample to be fabric, the sample size is 40mm×100mm.
- Plain color samples
According to the requirements of the standard for the size of the sample, the sample is randomly cut along the warp or weft direction of the front of the fabric. But it is required that the sample must be taken from a large sample that is uniformly dyed, wrinkle-free and can represent batch dyeing. The distance from the edge of the cloth should not be less than 10cm so that the entire working surface can produce consistent results during the test.
- Yarn-dyed samples
According to the standard for the size of the sample, it is required that the sample can contain all the colors of the sample. Suppose a sample cannot contain all the colors of the sample. In that case, the sampling amount can be determined according to the proportion of each color of the sample, and the dark part is preferred, or the number of samples taken can be increased, but generally not more than three sets of samples.
Richer colors characterize this type of product. Printed samples include small prints, large prints, inter-color stripes, etc. The basic principle of sampling is to take the excavation method to take all the colors and pay attention to keeping the same color parts around the sample as the original sample for rating comparison when excavating. If a sample cannot contain all the colors, you can increase the number of copies or determine the sampling amount according to each color’s proportion and give priority to the dark color test. The following is a detailed analysis of various samples.
①Single cycle small printing
When sampling a single cycle small print, try to ensure that the sample is sampled on a complete print. Sometimes, due to the influence of the color paste prescription, printing process and fabric structure, the print of the same pattern will also have a certain color difference. Sampling should be taken by digging. When digging, keep the same color around the sample as the original sample for the rating comparison after the test.
② No circulation and irregular small prints all over the floor
This type of sample has rich colors. Before sampling, you must first observe the sample and select a representative place with uniform dyeing to pick the sample. Often, one sample cannot contain all colors, then the number of samples should be increased.
③Large printing without circulation
Among the samples submitted by customers for inspection, such as some bedsheets, quilts, etc., these samples are characterized by relatively large margins and relatively large prints. The color of each flower type of this kind of sample is different. Usually, a sample can not cover all colors. In this case, it is necessary to pick the sample in a relatively dark position. Moreover, it is necessary to consider the ratio of each color to a certain ratio of dark and light to sample. It is impossible to pick up only the dark position because there may be dark and light color migration during the test. So, not only must the staining of the sample be considered when sampling, but also consider the discoloration of the sample.
④A large circular printing
This type of sample is usually rich in color, but it is cyclic. Just pick a sample from one of the looped patterns. Also, if other colors are not available, consider increasing the number of samples.
⑤ Inter-color stripe printing sample
The color of all strips should be included in the sampling within the specified sample size. Since the Color Fastness to soaping is a rolling test, which is different from the static test of the Color Fastness to sweat, there is no specified pressure requirement. When sampling, it is unnecessary to take samples in the direction of the strip as long as all colors are collected. Suppose a sample cannot contain all colors. In that case, you can increase the number of copies or determine the sampling amount according to the proportion of each color, and take priority to take the relatively dark part for testing.
5.4 Testing for thermal sublimation (dry heat) of textiles
5.4.1 Comparison of the main test methods for the Color Fastness to heat pressure and ironing of textiles:
The operation process of the standard three test methods is roughly the same. The preparation tools are as follows:
5.4.2 Take the AATCC Color Fastness test method as an example:
This test method is a test method to determine the color resistance of various textile materials and textiles and the ability of heat-resistant roller processing.
Textiles can be subjected to hot press tests in dry, wet, and wet states, usually determined by the textile’s final use.
- Sample size:
AATCC 133-2009: 40*120mm (sample size for other test methods: 40*100mm)
- Heating device:
It is composed of a pair of smooth parallel plates equipped with a precise control electric heating system. The pressure of the sample is 4±1kpa. The heat should only be transferred from the upper parallel plate to the sample. Regardless of if the lower parallel plate is heated or not, the asbestos plate should always be covered. The m2 two-layer synthesis contains about 3mm thick wool flannel, undyed and bleached cotton fabric without mercerizing treatment.
- Test procedure
Dry pressing: The dry sample is pressed for a certain period of 15 seconds in a heating device at a specified temperature and pressure.
Tidal pressure: After the dry sample is covered with a wet cotton lining fabric, it is pressed for a certain period of 15 seconds in a heating device at a specified temperature and pressure.
Wet pressing: After the wet sample is covered with a piece of wet cotton lining fabric, it is pressed for a certain period of 15 seconds in a heating device at a specified temperature and pressure.
- Hot pressing temperature
110 ± 2℃
150 ± 2℃
200 ± 2℃
If necessary, different test temperatures can be used, but they must be noted in the report. The critical temperature is determined according to the type of fiber and the structure of the fabric. If it is a blended product, it is recommended to adapt it to the most heat-resistant fiber.
Immediately after the test, use the grayscale to evaluate the sample’s color change and the staining of the lining fabric. Make another assessment after 4 hours of humidity control in a standard atmosphere.
5.4.3 Regarding ironing Color Fastness, ironing tips in daily life:
- Before ironing clothes, be aware of the fabric characteristics of the clothes, because some fabrics are not resistant to high temperatures, while others are. For instance, natural fibers like silk and wool are not suitable for high-temperature ironing, while textiles such as cotton and linen are.
- For some special fabrics, it’s advisable to iron directly on the fabric’s surface, and the fabric will be shiny and white. At this time, you only need to cover the surface of the fabric with a piece of lining cloth or cloth of the same texture and then iron; it will not appear in this case.
- Before ironing, it is best to spray the clothes evenly with water mist with a sprayer and put the clothes in a plastic bag so that the moisture can be spread evenly, and the clothes will be ironed better.
- Hang the ironed clothes in a ventilated place to dry for a while to evaporate the water vapor, so that the clothes can be kept flat and mildewed.
5.5 Color Fastness to perspiration
As we all know, the composition of human sweat is complex, the main component of which is salt, of which the amount varies from person to person. Sweat is acidic and alkaline. The short-term contact between textiles and sweat may have little effect on its Color Fastness, but long-term contact with the skin and sweat will have a greater impact on certain dyes. Clothing with unqualified Color Fastness is likely to cause dyes to transfer from textiles to human skin through sweat. The human body may absorb dye molecules and heavy metal ions through the skin, and this would endanger health.
5.5.1 Comparison of test methods for Color Fastness to perspiration
5.5.2 Examples of testing methods for textile sweat resistance
Use artificial sweat to simulate the condition of sweating to test textiles.
First, cut a certain number of 4mmX10mm test samples according to the project requirements, then sew the lining according to the sample type, and then put them into the petri dish, as shown in the following figure:
Then add the freshly prepared sweat stain solution (Figure 3, Figure 4) and soak for 30 minutes (Figure 5) (Human sweat has a complex composition, sweat is acidic and alkaline, and dyes in textiles are not acid-resistant while some are not alkali-resistant. Under the same conditions, artificial sweat with different acid and alkali levels needs to be tested separately).
After the soaking is completed, take out and scrape off the excess sweat, and sandwich it between the two sample plates. Use the same procedure to combine the samples and stack them together. After stacking them, place them between the sweat rack and the spring pressure plate, put a weight on the spring pressure plate (as shown in Figure 6) and take it away, pour out the excess sweat to form a combined test body.
Put the combined test body in a constant temperature oven for some time (Figure 7).
After taking it out, use the discoloration/staining gray card to evaluate the discoloration of the sample and the staining of the lining fabric (Figure 8).
5.5.3 How to improve the Color Fastness to perspiration? Examples of techniques for improving the Color Fastness of nylon fabric to perspiration
Weak acid dyes are mostly used in nylon printing and dyeing. It’s important to note that dyes and fibers are mainly combined with van der Waals forces and hydrogen bonds, which accommodates poor Color Fastness. Although the commercially available acid dye fixing agents can improve the Color Fastness to soaping and rubbing, it still lacks effective perspiration fastness fixing agent. Although the Color Fastness to acidic perspiration can be improved through sufficient soaping, dye selection, optimization of the fixation process and the development of new fixing agents or fastness enhancers, the Color Fastness to alkaline perspiration is still poor.
The improver of the Color Fastness to perspiration of acid dyes is still mainly the polyamide fixing agent that is a quaternary ammonium salt. The polyamine compound and dicyandiamide polycondensation reaction are mostly used to prepare the formaldehyde-free polyamide fixing agent, such as perspiration fastness Agent SF-30A, a polycationic fixing agent. Although the quaternary ammonium salt type polyamide fixing agent can significantly improve the perspiration fastness of acid dyes, it will significantly reduce the fabric’s rubbing fastness.
The purpose of this research is not to reduce the Color Fastness to rubbing, but to correspondingly improve the Color Fastness to the sweat of the quaternary ammonium salt type polyamide fixing agent. The test firstly measured the color fixation effect of perspiration fastness agent SF-30A, and then investigated the effect of perspiration fastness agent SF-30A and wet friction enhancer HS-222, adhesive SD-20B, and acrylate monomer comprehensive treatment on nylon Improved Color Fastness to rubbing and Color Fastness to perspiration of printed fabrics.
Fabric 380T nylon spun printed fabric, 20D/20D, areal density 35g/m2.
Perspiration fastness agent SF-30A (quaternary ammonium salt type polyamide, 30% solid content, self-made), adhesive SD-20B (copolymer of butyl acrylate and acrylic acid monomers, solid content 24%, Homemade), wet friction enhancer HS-222 industrial grade, chemical agent FMEE, ammonium persulfate and other additives.
1.2 Test method
1.2.1 Dipping finishing process
(1) Process flow
Nylon fabric → impregnation finishing liquid → centrifugal dehydration → drying → high-temperature baking → finished product
(2) Finishing fluid prescription/% (omf)
Perspiration fastness agent SF-30A x
Wet friction enhancer HS-222 y
Adhesive SD-20B z
(3) Sorting conditions
pH value 4.5~5.5 (adjusted by acetic acid), bath ratio 1:20, immersion at room temperature for 20 minutes, and baking at 160°C for 3 minutes.
1.2.2 Padding finishing process
(1) Process flow
Nylon fabric → padding finishing liquid → drying → high temperature steaming → drying → finished product
(2) Monomer emulsion
Mix 3% acrylate monomer, 0.75% emulsifier FMEE and 0.15% ammonium persulfate for high-shear emulsification. The emulsification time is 30min to prepare a monomer emulsion.
(3) Composition of finishing fluid
Add 4% perspiration fastness agent SF-30A to the above monomer emulsion, and adjust the pH value to 4.5-5.5 with acetic acid.
(4) Sorting conditions
Room temperature, double-dipping and two rollings, rolling rate 90%; high temperature steaming, humidity 40%, temperature 160℃, time 5 min.
1.3 Test method
(1) Color Fastness to rubbing
Test according to GB/T3920-2008 “Textile Color Fastness test Color Fastness to rubbing,” and according to GB/T251-2008, “Textile Color Fastness test grayscale for staining evaluation” rating.
(2) Color Fastness to perspiration
According to GB/T3922-2013, “Textile Color Fastness test Color Fastness to perspiration” test, according to GB/T251-2008 “Textile Color Fastness test evaluation staining grayscale” rating.
- Results and discussion
2.1 The influence of perspiration fastness agent on the Color Fastness of nylon
Nylon printed fabric adopts the impregnation finishing process in section 1.2.1. The mass fraction of perspiration fastness agent SF-30A on the Color Fastness to rubbing and Color Fastness to perspiration is shown in Table 1.
Table 1 The influence of mass fraction of perspiration fastness agent SF-30A on Color Fastness.
It can be seen from Table 1 that nylon printed fabrics have excellent dry and wet rubbing fastness and wool staining fastness to alkaline sweat, but the staining fastness of nylon to alkaline perspiration is poor; only Grade 2 to 3. After finishing with perspiration fastness agent SF-30A, it has no effect on dry rubbing fastness and alkaline perspiration Color Fastness of wool, which is still 4~5. However, it has obvious improvement to alkaline perspiration fastness nylon staining and increases with the increase of the mass fraction of SF-30A. The highest can be increased by 1.5 to 4, but it will cause the drop in the wet rubbing fastness in the warp and weft directions, and the drop in the wet rubbing fastness with the SF-30A finishing agent is related to the amount of SF-30A. When the mass fraction of SF-30A is 4%, the wet rubbing fastness will drop by two levels at most. This is because SF-30A finishing agent is a cationic polyamide quaternary ammonium salt with a good affinity with nylon and anionic acid dyes, and can form a film on the fiber surface. It also has good Color Fastness to alkaline perspiration. Therefore, it can improve the perspiration fastness to nylon staining, and does not affect the dry rubbing fastness and alkaline perspiration staining fastness of wool. The electrostatic interaction between cationic polyamide and acid dyes can reduce the resolution of acid dyes on the fabric in an alkaline medium. Still, it will cause acid dyes’ migration to the fiber surface when wet, that is, while improving the fastness of acid dyes to perspiration Reduced wet rubbing fastness. The acid dye used for fabric printing has excellent alkaline perspiration Color Fastness to wool.
2.2 The influence of perspiration fastness agent and wet friction enhancer
To improve the rubbing fastness of nylon printed fabric treated with perspiration fastness agent SF-30A, the finishing process in section 1.2.1 is adopted. The total mass fraction of the fixed finishing agent is 8%. The perspiration fastness agent is SF-30A. The enhancer HS-222 was mixed according to different mass ratios, and the influence of the two mass ratios on the Color Fastness of the fabric to rubbing and perspiration was investigated (Table 2).
Table 2 The influence of the mass ratio of perspiration fastness agent SF-30A and wet grinding enhancer HS-222 on the Color Fastness of fabrics
It can be seen from Table 2 that the perspiration fastness agent SF-30A and the wet friction enhancer HS-222 used in the same bath do not affect the wool staining and dry rubbing fastness of the nylon printed fabric; it is fast to alkaline perspiration, and the degree of nylon staining has been improved up to 2 levels; but the wet rubbing fastness still decreased, up to 1.5 levels. Comparison of Table 1 and Table 2 shows that when the amount of perspiration fastness agent SF-30A is the same, adding wet friction enhancer HS-222 is beneficial to improve the alkaline perspiration fastness, but it cannot improve the wet friction fastness. This may be because the wet friction enhancer HS-222 with crosslinking film-forming properties can improve the interaction between the polyamide cationic quaternary ammonium salt and the fiber, and improve the fastness to alkaline perspiration of the fixing agent. However, it will still cause the dye to migrate to the fiber surface in the wet state due to the water solubility.
2.3 The influence of perspiration fastness agent and adhesive
To improve the combination fastness of perspiration fastness agent SF-30A and nylon fiber, the finishing process in section 1.2.1 is adopted, and the total mass fraction of the fixed finishing agent is 8%. The perspiration fastness agent SF-30A and adhesive SD-20B in different mass ratios, were mixed to investigate the influence of the two mass ratios on the Color Fastness to rubbing and Color Fastness to perspiration. See Table 3.
Table 3 The influence of the mass ratio of perspiration fastness agent SF-30A and adhesive SD-20B on fabric Color Fastness
It can be seen from Table 3 that the use of the perspiration fastness agent SF-30A and the adhesive SD-20B in the same bath does not affect the wool staining fastness to alkaline perspiration and dry rubbing fastness of nylon printed fabric; it does not affect the nylon staining fastness to alkaline perspiration. The Color Fastness is improvable by 1.5 grades, and the impact on the wet rubbing fastness is small. When the mass fraction of the adhesive SD-20B reaches 6%, the wet rubbing fastness will not decrease. This is because the electrostatic effect of anionic SD-20B and cationic SF-30A can greatly develop the finishing agent’s binding fastness to the fiber, prevent the migration of acid dyes to the surface in the wet state, and ultimately improve the finishing agent’s resistance to alkali and sweat. However, it is relatively easy to gather during use and form a fixed stain. For this reason, although the use of nonionic surfactants to add O emulsification is beneficial to prevent aggregation, it is not good for improving the Color Fastness of alkaline perspiration nylon. Therefore, this method is still worthy of further discussion.
2.4 The influence of micro-polymerization of acrylic monomers
Acrylic adhesive is beneficial to improve nylon printed fabrics’ perspiration fastness and prevent the wet rubbing fastness from being reduced. Therefore, the emulsion of 18 acrylic monomers was selected to be finished in the same bath with the perspiration fastness agent SF-30A (according to 1.2.2. Section padding finishing process) to investigate the influence of different acrylate monomer polymerization on the rubbing fastness and perspiration fastness of the fabric. The results are shown in Table 4.
Table 4 The effect of acrylate monomer polymerization on the Color Fastness of fabrics
It can be seen from Table 4 that compared with the unfinished or single-perspiration fastness agent SF-30A, there is polymerization of acrylic monomers, (1) dry rubbing fastness and alkaline perspiration wool staining fastness, except for some single The body (ID-MA, TMPTMA, PEG200DMA, PEG400DMA, TMP3EOTA, DEGDMA, TEGDMA) is reduced by 0.5 level, and the Color Fastness of other monomers remain unchanged;
(2) The staining fastness of alkaline perspiration nylon is improved by 1.5 to 2.0 grades than that of unfinished fabrics, and 0.5 to 1.0 grades higher than that of SF-30A finishing alone;
(3) The wet rubbing fastness is 0.5~2.0 grade lower than that of unfinished fabrics. Except for some monomers (PHEMA, PEG400DMA and Di-TMPTA), the decrease is smaller than that of SF-30A finishing alone;
(4) Nylon fabric finished with BPA2EODMA, Di-TMPTA monomer and perspiration fastness agent SF-30A: Its alkaline perspiration fastness reached 4~5 grades, improved by two grades, and dry rubbing fastness remained unchanged at grade 4~5, but the wet rubbing fastness is slightly reduced, reaching Grade 4.
Acrylic monomers can undergo self-polymerization under initiators’ action and form a film on the surface of the fiber. Still, the nature of the film or the interaction with the perspiration fastness agent SF-30A and the fiber will affect the Color Fastness. This is because:
1) When finishing agent SF-30A exists alone, its fixing mechanism depends on ionic bond and film-forming properties. When the finishing agent SF-30A film formed on the fiber’s surface, it had better alkali resistance, it can prevent the dye from being in an alkaline medium. Analysis, reduce the re-staining (staining) of the fiber, improve the fastness to alkaline sweat, and also improve the fastness to dry rubbing. However, when the film formed by the finishing agent has good swelling properties, it will accelerate the resolution of the dye due to wet rubbing and reduce the wet rubbing fastness.
2) The structure of acrylate monomers contains vinyl groups, and polymerization reaction occurs under the initiation of ammonium persulfate. Acrylates can polymerize into polymers by themselves and form covalent interactions with fibers, finishing agent SF-30A, etc. It can improve its fastness to fiber and reduce the hydrophilicity and swelling of the SF-30A membrane. Therefore, the graft copolymerization of acrylic monomers on the fibers acts as a crosslinking agent, improving the wet rubbing fastness.
3) Due to the graft copolymerization of acrylate, the properties of finishing agent SF-30A and the fastness to the fiber are changed. This is related to the properties of acrylate monomers, such as Di-TMPTA monomers with four vinyl groups and BPA2EODMA monomers with bisphenol-A structure. Due to the increase in monomer reactivity or the introduction of the benzene ring structure, they can not only increase. It greatly improves the alkaline perspiration fastness and can also maintain excellent dry and wet rubbing fastness.
- The influence of monomer and Color Fastness additives on the Color Fastness of nylon fabric to perspiration:
(1) Cationic perspiration fastness agent SF-30A can improve the perspiration fastness of acid dyes, but it will reduce the rubbing fastness of dyes. When perspiration fastness agent SF-30A and wet friction enhancer HS-222 are finished in the same bath, it can inhibit the decrease of nylon printed fabric’s friction fastness.
(2) Cationic perspiration fastness agent SF-30A and anionic binder SD-20B are treated in the same bath, which can not only improve the perspiration fastness of acid dyes, but also have little effect on the rubbing fastness of nylon printed fabrics, but there is a tendency to aggregate insufficiently.
(3) The polymerization of acrylate monomers is beneficial to improve the rubbing fastness, but it is related to the monomer self-polymer properties. When choosing Di-TMPTA monomer with four vinyl groups or BPA2EODMA monomer with bisphenol-A structure and perspiration fastness agent SF-30A in the same bath, the nylon printed fabric has ideal Color Fastness, and alkaline perspiration is fast. The Color Fastness degree is 4~5, while the rubbing fastness is up to 4.
6. How to improve the Color Fastness of textiles (general rules)
The dye fastness of the fabric is related to fiber, yarn structure, fabric structure, printing and dyeing method, dye type and external force.
The following are the general principles for improving the Color Fastness of textiles. When it comes to individual Color Fastness, there will be targeted improvement methods.
Start with the following three aspects:
6.1 Selection of dyestuff
How fast a product is heavily dependent on the choice of dyestuff. If the choice of dyeing materials is inappropriate, no matter how good the auxiliary agent and the best dyeing process are, there is no way to dye high-quality Color Fastness. Only by choosing the right dye can we talk about the next step.
(1) Choose dyes according to fiber characteristics. Different types of dyes and fibers have different binding forms, and the strength of the binding bonds is also different. After the type of dye is determined, select dyes with high dyeing performance. For example, when dyeing wool fabrics, they are also strong acid dyes. Domestically produced strong acid dyes are not as good as imported strong acid dyes. Not only are the former not good in color, but their bonding strength is not as good as the latter. Different dyes have different binding fastness to wool and dyeing vividness. For example, the Color Fastness of wool yarn dyed with weak acid dyes is higher than that of strong acid dyes. In the case of pure cotton fabrics or regenerated cellulose fiber fabrics, either direct dyes (the category of dyes that are directly applied to cellulosic fabrics) or reactive dyes (a group of dyes considered to be the most permanent dyes because of their character of attaching to textile fibers and forming covalent bonds) can be used. In addition to acid dyes and some reactive dyes, individual direct dyes can also be used.
(2) Choose dyes according to the color depth. After determining the type of dye, it is necessary to further determine which dye to use according to the dyed color’s color system and depth. Try to choose dyes with shades close to the desired color. If there is a deviation, use other dyes to color. Secondly, look at the Color Fastness index of the selected dye itself. If the dye’s color fastness is poor, then the process can improve the Color Fastness by half. Finally, see whether the saturation of the dye can reach the required color depth. Choose a dye with a very low dyeing rate, even if the desired high-depth color can be temporarily achieved after processing. The dye’s combination will not be firm, and it will fall off during use reprocessing.
(3) Select the dye according to its Color Fastness grade. In the introduction of each dye, the Color Fastness grade of the dye is also introduced. When choosing a dye, you must choose the dye according to the Color Fastness grade required by the product, and the dye fastness of the matching colors’ dyes should be similar. For example, the dye’s Color Fastness can only reach 2~3, or even 1~2, no matter how good the auxiliary and dyeing process are, a product with 4~5 Color Fastness cannot be dyed. Because the dye’s Color Fastness mainly depends on the binding force between the dye and the fiber, if the bond between the two is not strong enough, no external force can make them bond firmly, even when the color is improved. They also would not withstand the damage of external factors such as washing and friction.
(4) The dye uptake rate of the fiber. Different dyes will exhibit different dye uptake rates, and under different dyeing conditions, the dye uptake rate of the same dye is also different. Therefore, the dyeing rate must be considered when choosing dyes. Otherwise, there will be competition between dyes. One of the dyes occupies the fiber’s dyeing position in advance so that other dyes can only be dyed on the surface of the fiber, not evenly. It forms a strong bond with the fiber, which is first destroyed in the subsequent process or daily use. That is why some colors fade and show a completely different color system from the original color. Therefore, when selecting dyes, dyes with similar dyeing speeds under the same conditions must be selected, which is also very beneficial to the next step of the formulation process.
(5) There should be good compatibility between dyes. Different dyes in the same fabric have different compatibility—the greater the compatibility value, the better the ability of dyes to match colors. There must be good compatibility between the dyes that match the colors. It is best to use the three primary colors for colors that are not easy to fight. The three primary colors have the best compatibility among each type of dyes, and they are also the three dyes with the most complete and most positive color matching. Therefore, it is best to use the three primary colors to match some of the more difficult, strange colors, and try not to use other dyes to fight. It is prone to competing for dyeing and dyeing flowers. 2.1.6 To minimize the number of dyes needed, first choose dyes whose shades are similar to the required colors when choosing dyes, and then use one or two dyes to supplement the lack of shades in the main dyes. For dyes of the same color series, the color dyed in this way should be pure, smooth, gorgeous and full. Try not to use four or five kinds of dyes for coloring, as it is not easy to color, neither is it easy to handle mass dyeing. Moreover, although the color and luster are matched, the dyed shade is not bright and full, and the dye cannot be fully combined with the fiber, resulting in poor Color Fastness.
6.2 Selection and use of additives
(1) Choose suitable additives. After determining the type of dye, the choice of additives is also very important. Generally, try to choose the auxiliary agent that matches with the dyestuff; if it is the common dyestuff used routinely, the determination of the auxiliary agent amount and usage method should be emphasized. For dark colors, the dye is not easy to be exhausted. The auxiliary agent can be added in batches to increase the exhaustion rate and improve the fastness of dye adsorption to play a role in fixing the color.
(2) Minimize the amount of retarder. The amount of retarding agent that plays the role of retarding dyeing should be reduced as much as possible. Otherwise, it will have the undesirable effect of stripping. On the one hand, it will reduce the dye uptake, and on the other hand, it will weaken the dye’s binding force and the fiber, making the Color Fastness worse. For colors that are easy to dye, the leveling effect can be achieved through the deployment of dyes and the heating speed.
(3) Selection of fixing agent. The use of a fixing agent will greatly improve the dye’s Color Fastness, generally at least 0.5~1 level, but the choice of fixing agent should also be based on the dye’s fastness, rather than just the individual items. For example, after reactive dyes are treated with cationic low-molecular-weight or polyamine-type fixing agents, the washing fastness of the fabric is 4~5, but the lightfastness will decrease. Furthermore, when fixing, the amount of fixing agent, fixing temperature and fixing time must be strictly controlled.
(4) Soaping and washing. When soaping and washing, you must wash thoroughly and pay attention to the washing temperature and time; otherwise, the floating color on the fabric’s surface will fade during use.
(5) Use of softener. To make the product plump and soft, it is necessary to add a softener. Softeners are categorically cationic, anionic, nonionic and silicone. Softening is the last process after the dyeing process. The dye and softener react furtherly, reducing the Color Fastness especially when the acid dye is dyed with organic silicon softener. Some of the dye will even be removed during the softening process. To lighten the color slightly. Therefore, the amount of softener used in softening treatment should be just right; otherwise, it will feel sticky and affect dyeing.
6.3 Next is to improve the dyeing and finishing process
Fully reduce the crystallinity of the crystalline part of the fiber macromolecular structure and increase the non-crystalline area’s crystallinity. The crystallinity of the various areas inside the fiber tends to be consistent. This is so that after the dye enters the fiber, the fiber’s combination is more-so evenly.
This can not only improve the level of dyeing but also improve the fastness to sublimation. If the crystallinity of the various parts inside the fiber is not balanced enough, most of the dye stays in the amorphous area with a relatively loose structure. After the extreme state of the external conditions, the dye will be more easily separated from the amorphous area inside the fiber and sublimated to the fabric’s surface, thereby reducing the sublimation fastness of textiles.
The scouring and mercerizing of cotton fabrics and the pre-shrinking and pre-sizing of polyester fabrics are all processing procedures that balance the fibers’ crystallinity. After scouring and mercerizing cotton fabrics and pre-shrunk and pre-shaped polyester fabrics, the dyeing depth and Color Fastness can be significantly improved.
Strengthening the post-treatment and washing and removing more surface floating colors can also significantly improve the fabric’s sublimation fastness. Appropriately lowering the set temperature during the setting process can significantly improve the sublimation fastness of the fabric. Reduced fabric dimensional stability due to cooling can be compensated by appropriately reducing the setting speed. When choosing finishing agents, attention should also be paid to the influence of additives on Color Fastness. For example, after using cationic softeners for the soft finishing of polyester fabrics, the thermal migration of the disperse dyes may result in the sublimation fastness test of the disperse dyes failing. From the perspective of the temperature type of disperse dyes, high-temperature disperse dyes have better sublimation fastness.
To sum up:
Many factors affect the dyeing fastness of textiles. For internal factors, all production processes are in place to ensure that the product can have excellent Color Fastness indicators to meet the requirements of daily use and reprocessing; for external factors, We must pay attention to the washing temperature, detergent and washing method, friction strength, exposure time and other factors that can reduce the Color Fastness according to the use requirements of the product, so that the product can be used better.
7. Common Q&A for Color Fastness testing
Q1. When the knitting product standard does not specify the friction sampling requirements, is the horizontal assessment evaluated?
(1). If the product standard stipulates that it is only straight, it should be implemented according to the standard;
⑵. Sampling requirements are not specified in the product standard, and both vertical and horizontal measurements are taken
Try to test every color as much as possible, and remark those that cannot be tested horizontally.
Q2. How is the Color Fastness to rubbing of woven fabrics evaluated when it is stated in the standard for knitted products that only the vertical direction is evaluated?
The woven fabrics are assessed in the warp and weft directions.
Q3. In GB/T 14576-1993 “Textile Color Fastness Test, Lightfastness and Perspiration Composite Color Fastness,” how should the rating be determined when the sample is unevenly discolored after the test?
According to the most severe discoloration rating.
Q4. SN/T 0309-1994 “Methods for the Inspection of Fluorescent Substances in Imported and Exported Textile Materials,” under ultraviolet light, the fabric has a bit-like, strong fluorescent luster (non-removable impurities). Can this situation be defined? Does it contain fluorescent substances?
It is defined as containing fluorescent substances.
Q5. For multi-component fiber textiles, choose lining fabrics. Can fibers of the same category fall into one category? For example, Fabric fiber content: 45% cotton, 25% polyester, 15% wool, 15% rabbit hair. Can wool and rabbit hair be classified as wool, and cotton and wool should be used for single fiber lining?
When choosing lining fabrics, fibers of the same category can be classified into one category, and lining fabrics can be selected according to corresponding standards.
Hemp: ramie, flax, jute, kenaf, etc. viscose, modal, lyocell, Cupra, etc.; wool: wool, rabbit hair, mohair, etc.; silk: mulberry silk, tussah silk Wait.
Q6. Since the test temperature of Color Fastness to washing is selected according to the composition, can the surface and lining be tested only according to the fabric’s composition when testing the garment?
According to the standard requirements, the washable temperature of the fabric and lining is selected according to their respective components.
Q7. After narrow-striped fabrics, printed fabrics, and yarn-dyed fabrics undergo Color Fastness tests (water resistance, perspiration resistance, soaping resistance), the samples’ degree of discoloration after the test is different. How to grade and judge?
When preparing samples, take the darker color as much as possible on the dark and light parts. Multiple combined samples can be cut and graded and judged according to the most severe discoloration for multi-color fabrics, wide and narrow striped fabrics.
Q8. GB 12982-2004 “National Flag” If the customer cannot provide radiant energy, how to determine the end of exposure?
Refer to 7.2.3 (Method 3) of GB/T 8427-1998 “Textile Color Fastness Test Color Fastness to Artificial Light: Xenon-Arc.”
Q9. There is no clause 6.2.3 in GB/T 8427-1998 “Textile Color Fastness Test Color Fastness to Artificial Light: Xenon-Arc” standard. Does the GB 12982-2004 lightfastness test method correspond to 7.2.3?
The lightfastness test in GB 12982-2004 shall be implemented in accordance with 7.2.3 in GB/T 8427-1998.
Q10. During the Color Fastness test of woolen fabrics, there are spots and stains. How to rate it?
According to the deepest spots.
Q11. During the test of Color Fastness to perspiration and water fastness, water stain marks appear on the samples after the test, and the water stain marks disappear after rubbing by hand. How to rank?
After removing the watermark, grade it.
Q12. How to choose a lining for the Color Fastness test of silk and acetate fiber blended fabrics?
Single fiber lining is used according to the following standards: GB/T 7568.8-2014 “Textile Color Fastness test standard for lining fabrics Part 8: Diacetate fiber” and GB/T 7568.6-2002 “Textile Color Fastness test wire standard sticker Lining fabric specifications.
8. Reasons for poor Color Fastness of silk fabrics and their care
The major component of silk fabrics is natural protein fibers. This feature makes it more breathable and softer than other fabrics. But also because of this characteristic, the mulberry silk fabric has an insurmountable shortcoming. That is, the Color Fastness is not high.
Proteins don’t do well at high temperatures, so mulberry silk fabrics cannot accept high-temperature processing. In the dyeing process, high-temperature dyeing and high-temperature fixing cannot be carried out. This is a major reason why its Color Fastness is not high.
Furthermore, protein is easily damaged in an alkaline environment, so acid dyes are generally used for dyeing. The fabric dyed with acid dyes is bright and full, but the Color Fastness is not high.
A large part of silk fabric colors is bound to fade. This includes lighter shades of light yellow, silver-gray, pink, light green, light blue, etc., and silk clothes of these colors are not resistant to sunlight. Among the silk fabrics of medium shades, most brighter colors are easy to fade, such as gold, orange, light green, brilliant blue, brilliant pink, ground red and the likes. The worst colors are gray and certain dark colors, such as grass green, various types of gray, brownish yellow, camel and the likes. Most dark silk clothes are easier to fade, especially red, purple, brilliant blue, plum green, etc. They are almost bound to fade.
Detergent selection: Chemical detergents are generally not suitable for silk fabrics. If it is underwear or contains dirty stains, it is recommended to use a neutral bath liquid for washing.
Water temperature control: high water temperature is the second killer of silk fabrics. When washing, do not use hot water soaking, be sure to use cold water at room temperature, and avoid soaking for a long time. Otherwise, it will cause the silk to turn yellow or fade. If you use hot water and soak for a long time, it would even stain the whole pot of water!
Method of scrubbing: Silk fabrics are different from pure cotton and chemical fiber fabrics. No silk fabrics can be machine washed. When washing at home, you must use hand wash and do not rub vigorously. It is advisable to use “washing” or “rinsing.” Wherever you can, use a soft towel dipped in the detergent to wipe gently, preferably not scrubbing.
Final drying: Silk has poor light resistance, and long-term absorption of ultraviolet rays will cause yellowing and hardening. Therefore, when drying, you must avoid direct sunlight and place the reverse side of the clothes in a cool place. When they are 80 to 90% dry, take them off and iron them with a medium-low temperature iron to keep the clothes shiny and durable. Also, avoid spraying water when ironing, and ensure to not iron it from the front to avoid water stains.