In the dyeing process of silk floral trousers, color fastness is a core indicator determining product quality, requiring comprehensive control from multiple dimensions, including dye selection, dyeing methods, process control, post-treatment techniques, and quality inspection. The way dyes bind to fibers directly affects color fastness. While natural dyes are environmentally friendly, their molecular structure is relatively unstable, necessitating the use of mordants to enhance their affinity with silk. For example, sappanwood dyeing requires the use of metal salts such as alum and ferrous sulfate to form complexes with the dye molecules, improving wash and lightfastness. Reactive dyes, on the other hand, contain active groups that can covalently bond with the amino and hydroxyl groups in silk, forming a stable chemical structure. Their wash and rubbing fastness is significantly better than that of weakly acidic dyes, making them more suitable for the intricate dyeing requirements of floral patterns.
The choice of dyeing method for silk floral trousers must match the fabric characteristics and pattern complexity. Immersion dyeing, as an intermittent process, uses a circulating dye bath to evenly adsorb the dye onto the fiber surface, then diffuses and penetrates into the interior. This method is suitable for large-area monochrome or gradient floral patterns. This process requires strict control of the liquor ratio and dyeing depth. A smaller liquor ratio reduces water consumption but can easily lead to uneven dyeing. Dyeing depth is adjusted by the ratio of dye dosage to fabric weight; darker colors require increased dye concentration and extended dyeing time. Pad dyeing, as a continuous process, removes excess dye liquor through roller pressure, followed by steaming or baking for color fixation. It boasts high production efficiency but is highly selective for dyes, necessitating the selection of fast-dyeing reactive or disperse dyes to ensure dyeing is completed within a short time (a few seconds to tens of seconds) and avoid color differences and floating color issues.
Precise control of process parameters is key to improving color fastness. Temperature directly affects the activity of dye molecules and the degree of fiber swelling. Reactive dye dyeing requires a temperature of 60-80℃; too low a temperature results in insufficient dye uptake, while too high a temperature damages the fiber structure. pH adjustment must match the dye type. Weakly acidic dyes require a weakly acidic bath with a pH of 4-4.5. At this temperature, the dye binds to the fiber through partial ionic bonds, hydrogen bonds, and van der Waals forces. If dyeing is done in a neutral bath, the fiber carries a negative charge and relies on hydrogen bonds and van der Waals forces, resulting in a significant decrease in colorfastness. Time control must balance dyeing rate and fixation efficiency. Too short a dyeing time results in insufficient dye penetration; too long a time may cause fiber damage or color shift.
Post-treatment techniques for silk floral trousers are crucial for improving colorfastness. Washing removes surface dye and unbound dye, reducing the risk of fading during subsequent use. It requires phased control of water temperature and detergent concentration; for example, first rinse with cold water to remove surface dye, then deep clean with warm water and a neutral detergent. Color-fixing treatment involves adding color-fixing agents (such as polyamines and quaternary ammonium compounds) to form insoluble complexes with dye molecules, blocking the water-soluble groups of the dye and improving wash and rubbing fastness. The amount of color-fixing agent used is generally 1.5-3 times the amount of dye; excessive amounts may cause the fabric to stiffen or change color.
Quality testing is the last line of defense to ensure color fastness. The color fastness to washing test simulates a daily washing scenario. The sample is sewn with a standard lining fabric and washed at a specified temperature, time, and detergent concentration. The degree of color change in the sample and staining of the lining fabric is evaluated. Underwear silk products usually require a grade of 3-4 or higher. The color fastness to rubbing test assesses the staining grade of the lining fabric through dry and wet rubbing tests. Clothing silk must be at least grade 3. The color fastness to light test exposes the sample to simulated sunlight and compares it with a standard blue wool fabric to determine the grade. Outdoor silk must have good light fastness.
