Popular science | Dyeing and finishing process and key points of polyester and polyurethane warp knitted stretch fabrics

grey fabric unwinding-preshrinking (dry cleaning or washed) – pre-styling – dyeing – finished product re-styling – inspection – packaging

During the weaving process, the polyester-span elastic fabric undergoes greater tensile deformation due to tension. Although spandex has good elastic recovery capabilities, there are still large deformations caused by partial slow elastic deformation inside the gray fabric. Residual stress deforms the fabric structure, which in turn affects the control of quality indicators such as width and surface density, and affects post-finishing processes such as dyeing and shaping.

The purpose of pre-treatment is to fully relax and pre-shrink the fabric, eliminate the residual stress inside the fabric, especially the spandex yarn to fully shrink Shrink, reduce or eliminate the surface density and density difference between the left, middle and right sides of the fabric, and inside and outside the roll. At the same time, it can remove a large amount of fiber oil on polyester and spandex yarns, as well as oil stains or other stains on the fabric during the weaving process to facilitate subsequent progress of work.

The scouring process of polyurethane elastic fabrics includes washing and dry cleaning. At present, water washing is basically used, and water washing equipment is used. It is cost-effective, its price is about one-third of dry cleaning equipment, and the washing efficiency is 15%-20% higher than dry cleaning; water washing can wash more types of stains than dry cleaning, such as sweat stains when transporting gray cloth, while dry cleaning is more sensitive to oil stains The washing ability is strong; washing water consumption is large, and dry cleaning causes greater pollution to the environment; the washed gray fabric needs to be pre-shaped immediately, otherwise creases will appear on the cloth surface.

The washing speed of polyester-span elastic fabric is close to that of nylon-ammonium fabric, generally 20-22m/min, washing temperature And the holding time varies depending on the additives selected, generally it does not exceed 85%, the heating rate does not exceed 1℃/min, the cold water washing temperature does not exceed 40℃, the time is 30min, and the cooling rate is 1℃/min.

In polyester and spandex warp-knitted stretch fabrics, the spandex yarn is wrapped inside the fabric by polyester yarn, so it can be heat-set like polyester and can generally withstand short-term dry heat treatment below 190°C. .

Polyester and spandex elastic fabrics must be padded before pre-shaping. The purpose is to eliminate as much as possible through the antioxidant treatment of the anti-yellowing agent GR. For color strips in dyeing, penetrants and defoaming agents can be appropriately added as needed. The pre-setting process conditions are generally 190°C and the speed is 19-21m/min; the setting machine uses a 10-section oven, and the temperature in the first 4 sections is low for pre-setting. The drying area can be set to 160℃, 160℃, 170℃, and 170℃ respectively; the oven temperature in the last four sections is set to 190℃, and the oven temperature in the last two sections is set to 180℃; generally, the air volume at the bottom of the setting machine is larger than that at the top. The air volume is large, as long as the cloth surface does not touch the upper air outlet or the lower air outlet; the door width is generally about 155.2cm; the tension is about 14.7N; overfeeding is about 10%.

The above process parameters should be adjusted appropriately according to the gray fabric specifications and actual conditions during production. If the setting temperature is lower than 185℃, the door width size will be stable The elasticity of the spandex is not enough, and the fabric surface is prone to fold marks; if the temperature is too high, the internal molecular structure of the spandex will change, causing the elasticity of the spandex to be damaged, resulting in a reduction in the elasticity of the spandex and the formation of wind marks; therefore, the temperature of heat setting must be accurately and stably controlled. The degree of curling of gray fabric affects the fabric speed during shaping. The more severe the curling, the slower the fabric speed should be.

Polyester-styrene elastic warp knitted fabrics are generally dyed with disperse dyes in high-temperature and high-pressure overflow dyeing machines. The dyeing equipment for nylon elastic plain warp knitted fabrics is commonly used normal temperature rope dyeing machines and warp beam dyeing machines. Considering the influence of temperature on the elasticity of spandex in polyester and spandex fabrics, the dyeing temperature is generally set to: 120°C for light colors and 120°C for medium and dark colors. 125℃, reduction cleaning temperature is 80℃, holding time 40-60min, temperature rising and cooling rate 1℃/min.

Since the optimal pH value for disperse dye dyeing is 4.5-5.5, disperse dyes are unstable and have poor diffusion performance at a pH value of 7 or higher, and are prone to color Flowers and tar spots, therefore, choose a dye bath pH value of 5.0-6.0

The dyeing temperature should also be adjusted according to the quality of spandex yarn. Spandex The heat resistance varies with different manufacturers. It is generally 104℃-130℃. Therefore, it is usually around 120℃ to avoid the aging and fragility of spandex yarn due to high temperature. The spandex yarn is less affected by the heating and cooling rate, so the production The dyeing temperature is mainly determined by the leveling performance of the dye.

During the dyeing process, if the fabric runs fast, the cloth surface will be smooth and The level dyeing property is good, but due to the high tension on the fabric, the spandex yarn is easy to break; if the running speed is slow, the cloth surface is prone to wrinkles and chicken paw prints, and the level dyeing property is poor. The spandex yarn is protected during dyeing and is different from ordinary polyester varieties. In comparison, the rotation speed of the main pump of polyurethane elastic fabric is slightly slower.

Polyester and spandex stretch fabric for restyling When the temperature is 180℃, the cloth speed is 32-35m/min. The oven temperature in the first 4 sections is low and used as the pre-drying area, which can be set to 170℃ respectively. The oven temperature in the last 4 sections is set to 180℃. The tension is generally set to 29.4-34.3N, the temperature of nylon and ammonia fabric is 160°C, and the fabric speed is basically the same as that of polyester and ammonia fabric. The determination of process parameters should be adjusted according to the gray fabric specifications and actual conditions.

In addition, compared with nylon, since the shrinkage rate of polyester is smaller than that of nylon, if the same finished product area density is to be obtained in the end, such as 200g/ m², the polyester stretch fabric should generally reach 195-196g/m when disembarking², while the nylon elastic fabric reaches 193-194g/m².