Knitted fabrics are created by using knitting needles to loop yarns into interlocking loops. The key difference between knitted and woven fabrics lies in the distinct arrangement of yarns within the fabric structure. Knitting is classified into weft knitting and warp knitting. Today, knitted fabrics are widely used in apparel, lining materials, home textiles, and other applications, enjoying widespread consumer appeal. However, during the printing and dyeing processes, knitted fabrics often encounter a variety of challenges.

01 Colorfastness Non-Compliant

Color fastness includes lightfastness, soap-wash fastness, sweat-stain fastness, rubbing fastness, sublimation fastness, and ironing fastness. These properties are primarily determined by the structural characteristics of the dye, but are also closely related to the fiber type, dye concentration, dyeing and finishing processes, and external conditions. Therefore, ensuring that color fastness meets the required standards hinges first on the selection of dyes, followed by the optimization of dyeing processes and the appropriate use of auxiliaries.

When developing dyeing processes, it is essential to make well-considered decisions based on the dye, the fiber type, and the customer’s performance specifications, so that, with the aid of auxiliaries, the dye can be applied to the fiber as firmly as possible under appropriate conditions and achieve thorough fixation. With regard to auxiliaries, first, high-quality leveling agents and dye-promoting agents should be selected to ensure slow, uniform, and complete dye uptake; second, chelating agents should be added to prevent dye–metal ion complexes in the bath from causing floating color and to reduce hydrolysis of reactive dyes and other types in water; third, superior soap‑washing agents should be chosen to effectively remove floating color and to prevent such color from redepositing onto the fabric; and fourth, suitable fixing agents should be selected. At present, no truly ideal fixing agents are available for sublimation fastness or lightfastness; however, excellent fixing agents are readily available for other key properties such as soap‑wash fastness, sweat‑stain fastness, and rubbing fastness.

02 Poor rubbing fastness

Rubbing fastness refers to the degree of color loss in dyed or printed fabrics after rubbing, and it is classified into dry rubbing and wet rubbing. Rubbing fastness is evaluated based on the extent of color transfer to a white cloth, with a rating scale from 1 to 5; the higher the score, the better the rubbing fastness.

When a dyed fabric is rubbed against a white test cloth, the extent of color transfer from the fabric to the test cloth—or vice versa—is influenced by several factors. There are two primary mechanisms for color transfer: first, dye molecules detach from the fabric or fade, thereby staining the test cloth; second, colored fibers fray and break into fine pigment particles that adhere to the surface of the test cloth. In practical applications, dye detachment is the dominant mechanism.

Although active dyes with different chemical structures exhibit varying degrees of covalent bond strength and adhesion to cellulosic fibers, their impact on the wet fastness of dyed fabrics is essentially the same. During wet rubbing, the covalent bonds between the dye and the fiber do not break, thereby preventing the formation of floating color. Floating color typically arises when dye molecules fail to form covalent bonds with the fiber and are instead adsorbed solely through van der Waals forces. One of the primary causes of floating color is the excessive addition of dye. Under wet conditions, the amount of color transferred is nearly linearly related to the dyeing depth: deeper shades require higher dye concentrations, but these should never exceed the saturation level. Excess dye that cannot bind to the fiber will accumulate on the fiber surface as floating color, severely compromising the fabric’s wet rubbing fastness.

The directness and diffusivity of dyes are also closely related to their rubbing fastness. Reactive dyes with high directness, although exhibiting high dye uptake and fixation rates, have poor diffusivity and thus struggle to penetrate deep into the fiber, leading to the formation of unfixed dye on the surface. Such unfixed dye is difficult to remove during washing, resulting in poor rubbing fastness. In contrast, dyes with good diffusivity can readily penetrate the fiber, which helps improve rubbing fastness and enhances wash fastness. On the other hand, dyes with poor stability, even after surface unfixed dye has been washed away, may see hydrolyzed dye leach out from within the fiber over time, thereby compromising both soap-washing fastness and rubbing fastness.

The diffusion rate and penetration depth of dyes vary depending on the fiber’s structural characteristics, resulting in differences in color fixation efficiency and dye diffusion among fibers. Higher color fixation rates correspond to lower levels of hydrolyzed dye, easier washability, and improved rubbing fastness; moreover, a smooth fiber surface with a low coefficient of friction also enhances rubbing fastness.

The order of friction coefficients for several common fabrics is as follows:

Plain-weave fabrics > Twill fabrics > Satin fabrics

Some thin fabrics—whether synthetic or made of real silk—have a relatively loose weave. Under dry rubbing conditions, the fabric sample tends to slide along with the friction head due to the combined effects of pressure and friction. In the wet state, however, these fabrics exhibit very low hygroscopicity, with minimal swelling and even a lubricating effect, resulting in superior wet rubbing fastness compared with dry rubbing fastness.

Pre-treatment has a significant impact on the rubbing fastness of fabrics. Untreated cotton fibers swell under wet conditions, increasing the coefficient of friction and reducing fiber strength, which can lead to the breakage and detachment of dyed fibers and the formation of color specks. Therefore, appropriate pre-treatment prior to dyeing—such as mercerization, singeing, and cellulase treatment—can improve the smoothness of the fabric surface, reduce frictional resistance, and minimize floating dye, thereby effectively enhancing wet rubbing fastness.

03 Wrinkle Issue

The primary causes include equipment-related factors, as well as issues related to the amount of fabric loaded, the liquor ratio, and process operations. Differences in equipment—such as the loading capacity per tube, the pressure and friction between fabric layers, pump power, and the intensity of mechanical action—all affect the flatness of the fabric surface. The liquor ratio also plays a role in fabric smoothness, and excessive foaming from auxiliaries during processing can lead to fabric floating, while abrupt temperature changes during heating and cooling can induce fine creasing. Currently, bath lubricants, anti-crease agents, and softening agents can all help mitigate fine creasing; however, unless the equipment is improved and process control is optimized, simply adding bath lubricants cannot completely prevent the formation of fine creases.

04 Phoenix Seal or White Seal

Wind marks generally refer to a type of dyeing defect that occurs in textile fabrics after printing and dyeing during the drying and storage processes. Compared with the normally dyed, undyed fabric, wind-marked areas exhibit long, white or dull gray streaks running across nearly the entire width of the fabric in the weft direction. This defect is not visible before setting but becomes apparent after the setting process.

A discoloration phenomenon that occurs on the edge portions of fabric in contact with air during the stacking process after dyeing but before color fixation, particularly with certain types of reactive dyes (such as sulfate ester ethyl sulfone-type dyes).

Wind marks generally refer to a type of dyeing defect that occurs in textile fabrics after printing and dyeing during the drying and storage processes. Compared with the normally dyed, undyed fabric, wind-marked areas exhibit long, white or dull gray streaks running across nearly the entire width of the fabric in the weft direction. This defect is not visible before setting but becomes apparent after the setting process.

Polyester fabrics are less prone to wind marks during continuous production on long-line dyeing machines, but they are more susceptible to wind marks in batch production, particularly during high-temperature, high-pressure overflow dyeing. In polyester fabrics, wind marks typically occur during the stage between fabric dehydration and spreading and before setting, often appearing as repeated fold marks left by the fabric being stacked and folded on the stacker. In severe cases, dozens of such marks may be visible across the weft direction, with the spacing exactly corresponding to the pitch of the fabric’s back-and-forth folding.

The cause of “wind marks” in non-paste-coated polyester woven or knitted fabrics is as follows: During the waiting period after the fabric is spread out following weaving, the areas subjected to repeated folding are exposed to the air. The airflow causes the moisture in these folded regions to evaporate and dry first. Due to capillary action, free water from other parts of the fabric migrates toward the folded areas. However, antistatic agents and lubricants added during spinning and weaving, as well as leveling agents and detergents used in post-dyeing treatments, leave behind small residual amounts in the fabric and in the free water it carries; most of these auxiliaries are nonionic. Analogous to the mechanism of dye migration, when free water flows into the folded regions, the residual auxiliaries dissolved in that free water also migrate toward the folds.

As moisture continues to evaporate, the concentration of processing aids at the pleat folds becomes much higher than in other areas. During high-temperature setting, the thermal migration of disperse dyes from the pleat folds is significantly greater than from other regions. This phenomenon arises because the processing aids on the fiber surface dissolve at elevated temperatures, enabling the dyes to migrate from the fiber interior through capillary action to the fiber surface, where they accumulate and give rise to a series of adverse effects. These include changes in color shade, as well as reductions in colorfastness to rubbing, washing, perspiration, dry cleaning, and sunlight exposure. Most critically, however, is the pronounced difference in color shade between the pleat folds and the rest of the fabric—commonly referred to as “wind marks.”

The formation of “wind marks” in sized polyester woven fabrics differs from that in unsized polyester woven or knitted fabrics in that the sizing process for the former involves a longer dyeing and finishing sequence, during which most of the processing aids used in spinning and weaving have been removed. Nevertheless, trace amounts of auxiliaries employed in dyeing and subsequent treatments may still remain on the fabric and in the free water it carries. Furthermore, although the desizing step includes two hot-water washes and one acid wash, residual caustic soda from the desizing process may persist in the individual polyester fibers, even within the amorphous regions.

Similarly, during the stacking and waiting period before fabric setting, free water can carry residual alkali and auxiliaries to the areas of repeated folding. At this stage, the pH in these folded regions is markedly more alkaline than in other parts of the fabric, a finding confirmed by universal indicator tests; moreover, the concentration of auxiliaries in these folded areas is also higher than elsewhere. During high-temperature setting, the polyester macromolecular chains undergo vigorous motion, allowing OH– ions to rapidly penetrate the amorphous regions along with water molecules and react with disperse dyes.

Disperse dyes are generally stable under acidic conditions (pH 5). Under alkaline conditions, however, two main effects typically occur: first, the alkaline environment can induce deprotonation and dissociation of the dye molecule; this reaction is reversible, and the undissociated structure will re-form in neutral or slightly acidic media. Second, alkali can promote hydrolysis of certain disperse dyes; following hydrolysis, not only does the color shade change, but the dye’s affinity for the fiber also alters. Consequently, alkali can cause irreversible degradation of some disperse dyes.

Therefore, the color change at the fold lines of sized polyester woven fabrics is caused by the combined effects of excessive pH, hydrolysis or ionization of disperse dyes, and thermal migration of disperse dyes induced by auxiliaries.

05 Ways to Prevent Wrinkling in Polyester Fabrics

If the two fabrics mentioned above are promptly dewatered, spread out, and set after exiting the dyeing vat, wind marks generally do not occur. However, if they are left to stand for a period of time—approximately 30 hours—before setting, wind marks are more likely to develop. To fundamentally eliminate wind marks, it is essential to start with the underlying mechanisms that cause them and minimize all contributing factors.

The primary cause of “wind staining” in textiles is related to the dyes used. Typically, a small number of vat dyes, naphthol dyes, certain vinyl sulfone-type reactive dyes, and the vast majority of direct dyes exhibit poor fastness to sunlight and oxidation, making them prone to wind staining. In addition, some reactive dyes are highly sensitive to alkali; if the alkali is not thoroughly removed from the fabric after dyeing, wind staining can easily occur when the pH exceeds 8—for example, with reactive turquoise KN-G and reactive brilliant orange G.

During the fixing process, wind marks are observed; however, at the repeatedly folded areas of the unfixed fabric, high concentrations of auxiliaries or OH⁻ ions are physically adsorbed onto the fiber surface. Without high-temperature fixing, these auxiliaries cannot dissolve the dyes in the amorphous regions, nor can the OH⁻ ions penetrate the amorphous zones to react with the disperse dyes. Therefore, after washing or acid washing, the high concentrations of auxiliaries and OH⁻ ions at the folded areas are diluted. Repeated and timely fixing can thus prevent the formation of wind marks.

06 Brittleness Issue

Brittleness manifests as a reduction in tensile strength. Aside from pre-treatment-related brittleness—such as that caused by improper oxygen bleaching or other processing steps resulting in holes—brittleness during the dyeing stage generally stems from two main causes: first, photosensitive brittleness induced by dyes like sulfur black, which can be mitigated by adding anti-fragility agents; and second, the detrimental effects of strong reducing and oxidizing agents used in vat dyeing on fiber integrity. The second cause is improper acid usage during either the dyeing or neutralization stages; while glacial acetic acid is typically employed for neutralization, the market currently offers several substitute acids.

07 color spots (including white spots)

There are many causes of color spots; for example, white spots may result from immature cotton fibers that fail to take up dye, or from solid substances such as soda ash adhering to the fabric and causing localized areas to remain undyed.

The primary cause of color spots is:

• Improper dye selection: dye particles that are too large or prone to agglomeration can result in color spots;
• Poor dye dissolution: Undissolved dye enters the dye bath and adheres to the fabric, resulting in color spots.
• Poor water quality: Poor water quality causes dye aggregation;
• Equipment contamination: tar-like deposits in the dye vat fall off, resulting in color spots;

Auxiliary agent-related causes: The auxiliaries added during dyeing can sometimes cause the dye to aggregate, resulting in color spots; excessive foaming from the auxiliaries can lead to colored foam that adheres to the fabric and forms color spots; precipitated auxiliaries may combine with the dye and deposit on both the fabric and the equipment, with the resulting agglomerates on the equipment subsequently transferring to the fabric and causing color spots.