Timeless styling process: Fabric heat setting is usually a process of maintaining the fabric to a certain size under certain temperature and humidity conditions, heating it for a certain period of time and then cooling it. Therefore, the main process conditions for heat setting are nothing more than temperature, time, tension and swelling agent.
Temperature
Temperature is the most important factor affecting the quality of heat setting.
Because after the fabric is heat-set, the original wrinkles are eliminated to the extent that the surface The improvement of flatness, dimensional thermal stability and other wearing properties of fabrics are closely related to the heat setting temperature.
Polyester filament fabric
The refined polyester filament After the fabric is set at different temperatures, it is then placed at different temperatures for free shrinkage (i.e. dry heat shrinkage). The test results show that heat setting can improve the dimensional thermal stability of the fabric. The higher the setting temperature (120~220℃), the better. The lower the shrinkage of the fabric at the specified temperature (120~200℃). For example, the free shrinkage of unshaped fabrics and fabrics set at 120, 170, and 220℃ at 175℃ are 15%, 10%, and 5.5% respectively. ,1%.
If the fabric is required to have good dimensional thermal stability at 150°C, the setting temperature must be raised to 180°C, but continuing to increase the setting temperature will not affect the dimensional thermal stability of the fabric. There is no significant improvement. For example, even if the setting temperature is increased to 220°C, the fabric still has a free shrinkage of close to 1% at 150°C.
If the fabric needs to have good dimensional thermal stability at 175°C, the setting temperature needs to be increased to about 200°C. Continuing to increase the setting temperature, the free shrinkage rate of the fabric at 175°C is still around 1.5%, and there is no obvious improvement in the dimensional thermal stability.
So usually in order to ensure that polyester filament fabrics have good dimensional thermal stability at a certain specified temperature, the setting temperature is often 30~40°C higher than the specified temperature.
Nylon fabric
The situation of nylon fabric is similar. The area shrinkage percentage of nylon 66 warp knitted fabrics with a normal moisture regain of 4%, after heat setting at different temperatures, and then treated in 1 g/L soap solution at 200°F (93.3°C) for 1 hour As shown in Figure 2-1-6.
The higher the setting temperature, the higher the dimensional stability of the fabric.
Blended fabric
For blended fabrics, since the properties of synthetic short fibers are inherently different from those of filaments, and they are blended with other fibers, their thermal properties are basically similar to those of filament fabrics, but And it has its own characteristics.
Generally speaking, the dimensional thermal stability of polyester/cotton fabrics is higher than that of polyester filament fabrics. For fabrics that have been heat-set to a fixed length, if the setting temperature is higher than the free shrinkage temperature, It can have good dimensional thermal stability at 20°C. For example, polyester/cotton fabrics set at 200°C have a free shrinkage rate of 1.5% at 180°C.
For fabrics that need to be hot-melt dyed on a general guide roller hot-melt dyeing machine, the process conditions for heat setting before dyeing should be based on the specific conditions of hot-melt dyeing. With appropriate adjustments, the dimensional change rate in the warp and weft directions and the critical dissolution time (CDT) of polyester during hot-melt dyeing of unshaped polyester/cotton fabrics after being shaped at 180°C and 200°C are listed in Table 2- 1-13 in.
The so-called critical dissolution time (CDT) refers to the time from the beginning of contact with phenol until the polyester ring sample swells at the specified temperature Time required for disintegration (seconds). CDT is related to the crystallization state of polyester, including crystallinity, crystal size and crystal integrity, and can reflect the “heat history” of polyester.
The larger the CDT, the more severe the heat treatment conditions the polyester has experienced.
As can be seen from Table 2-1-13, the dimensional stability of heat-set fabrics during the hot-melt dyeing process is significantly improved compared to unset fabrics, and As the setting temperature increases, the dimensional change rate becomes smaller; although the CDT of polyester after hot-melt dyeing still has certain differences depending on their “heating history”, the differences between them (unset, 180°C and 200°C set) The gap is significantly smaller, mainly because when the hot-melt dyeing temperature is higher than the heat-setting temperature or close to it, it has a certain effect on improving the CDT of the fiber. If it is lower than the heat-setting temperature, the effect is not obvious.
The above results show that in addition to the beneficial effects of eliminating wrinkles on the fabric and ensuring uniform dyeing, heat setting before dyeing can also improve the size of the fabric during hot solution dyeing. stability.
If the process conditions for heat setting before dyeing are properly selected and the warp tension is reduced as much as possible during hot-melt dyeing, the fabric after hot-melt dyeing will be durable even without the final high-temperature tenter. It is also possible to have the required size and dimensional thermal stability of the finished product, which will help shorten the process, improve the feel of the finished product, and reduce the requirements for dye sublimation fastness, etc.
In addition to the size of the fabric, the setting temperatureAfter the temperature treatment, the intensity of the absorption peak with a wave number of 988 centi-1 was measured, as shown in Figure 2-1-8.
It can be seen from the figure:
(1) The number of refolded molecular chains increases as the heat treatment temperature increases;
(2) Tension hinders the refolding of molecular chains;
(3) When the temperature is very high, such as 220°C, The effect of tension in hindering chain folding is greatly reduced.
The above test results show that tension has a significant impact on the fiber structure, and the fiber structure There is a close relationship with performance. Therefore, it is important to pay attention to tension control during any shaping process.
Swelling agent
Is there any swelling agent on the fabric during heat setting? There is a certain relationship with the setting effect. The commonly used swelling agent is actually water or steam. For example, the presence or absence of moisture has a significant impact on the dyeing properties of nylon.
Compared with unshaped fibers, the diffusion rate of dyes in steam-set fibers increases, but decreases in dry-heat-set fibers.
The increase in the diffusion rate of the dye in the fiber after steaming and setting is not due to the increase in solution orientation or end groups from the fiber structure, but because of the formation of another fiber. caused by a supramolecular structure.
Figure 2-1-9 shows the NMR test results of fibers after heat setting of nylon 6 under dry heat and wet conditions. It is already known that NMR tests can detect fibers. The content of macromolecular segments that move like fluids in a medium.
It can be seen from Figure 2-1-9 that moisture has a “loose” fiber structure. The effect of enhancing the fluid-like motion of macromolecular segments is obvious even at room temperature.
This illustrates the plasticizing effect of moisture during the heat setting process, thereby affecting the supramolecular structure and physical properties of the fiber. In addition, if you want to make the fibers have the same crystallinity after being set, during steam setting, due to the effect of moisture, the temperature can be lower than that of dry heat setting. Moreover, from the perspective of water absorption, their amorphous zone structure also has The difference is that the water absorption capacity of the fiber after steaming and setting is much higher.
During moist heat setting, tension also has an impact on the structure and physical properties of the fiber. Tension has the opposite effect on “loose” fiber structure.
The influence of moisture on the properties of polyester during heat setting is small, and is far less obvious than that of nylon. </p
