Determination of polyester shaping process
Polyester is a thermoplastic fiber that can be used in a series of dyeing and other processes During the processing, due to multiple mechanical actions and multiple stretches, the original width and coil geometry of the fabric are changed, resulting in deformation and shrinkage, and even horizontal strands being skewed, seriously affecting the quality of the product.
The main purpose of heat setting is to heat the polyester knitted fabric under tension, and bake the fabric at a specified temperature to intensify the thermal motion of the secondary bonds between fiber molecules and molecular chain segments, so that it can The molecules are reorganized and arranged, and the internal stress is relatively stable.
As a result, the dimensional stability of the fabric can be improved, the anti-wrinkle performance can be enhanced, and the surface finish, strength, anti-pilling and other properties of the fabric can also be improved.
Control two important points
The key to polyester knitted fabrics during the heat setting process is to control the setting temperature and setting time.
If the heat-setting temperature is too low and the time is too short, it can cause defects such as unevenness, stiffness, and shrinkage of the fabric surface, and the setting effect will be lost; if the heat-setting temperature is too high or the time is too long, the fabric will become stiff. It becomes brittle, the strength decreases, the elasticity decreases, and some disperse dyes can be sublimated to cause color difference. In severe cases, the fibers can even melt.
Polyester setting time calculation formula
Practice has proven that the appropriate setting temperature for polyester knitted fabrics is 180- 210℃, setting time 20-90s, cooling temperature is about 50℃.
It can be calculated according to the following formula (calculated according to different shaping machine structures): shaping time (s) = shaping length (m) / fabric linear speed (m/min) × 60 various types of polyester knitted fabrics in Z921 On the needle plate tenter setting machine, when the setting temperature is 185-190℃, the linear speed is: polyester warp knitted mosquito net cloth 10-15m/min, polyester warp knitted shirt cloth 12-18m/min, polyester warp, weft, Knitted outerwear fabric 12-20m/min, polyester yarn-dyed jacquard fabric 7-10m/min.
When setting the shape, the “tension” and “overfeed” of the fabric should not be ignored and should cooperate appropriately.
If the width of the tenter exceeds the width of the fabric, it will cause an increase in shrinkage and a decrease in strength; if the overfeed is too large or the tension is unequal, it will easily cause weft wavy shapes. (commonly known as “fungus edge”), otherwise stripes will appear in the meridional direction. In short, process conditions such as width, tension, and overfeeding must be strictly controlled during the operation.
Expansion of shaping knowledge
The main purpose of pre-shaping is to eliminate wrinkles and slack generated during pre-processing Some crescent edges formed during the untwisting process stabilize the expansion and contraction changes in subsequent processing, improve the uniformity of molecular structure arrangement in the amorphous region of polyester macromolecules, reduce crystallization defects, increase crystallinity, and improve the uniformity of subsequent alkali weight loss. .
After the relaxed and shrunken fabrics are pre-shaped by dry heat, the style of the printed and dyed fabrics will be affected. Because in order to eliminate wrinkles and improve the uniformity of molecular structure arrangement, tension must be exerted on the fabric. The increase in strength will reduce the crepe effect, reduce flexibility, and deteriorate a series of properties such as softness, resilience, and fullness.
Attention: When setting, overfeeding and shrinkage can be used to compensate for the change in fabric style caused by increased tension. Tension will reduce the crepe effect, but it can improve the uniformity of weight loss and dimensional stability. For this reason, excessive tension during processing should be avoided after relaxation, so drying is generally not done before setting. If drying, loose drying equipment should also be used.
In order to avoid the disappearance of the crepe effect and affect the fabric style, the setting width is generally 4 to 5cm smaller than the finished product, or 2 to 3crn wider than the pre-processed width. The tension of the front guide roller is all relaxed, and an appropriate amount of Overfeed (such as increasing by 10% to 20%) to maintain the warp buckling and improve the fabric style; the cooling system ensures normal operation. To prevent creasing, melting and hardening.
Temperature control: The preforming temperature is generally controlled at: 180-190:C. The setting temperature is low, which is beneficial to the feel of the fabric, but wrinkles will increase due to moisture and heat. The weight loss rate and color yield change with the change of the setting temperature. Below 170~180℃, the weight loss rate and color yield decrease with the increase of temperature; at 190~230℃, the weight loss rate and color yield decrease. Color rate increases with temperature. Therefore, the preforming temperature needs to be selected based on the weight loss rate and fabric style requirements combined with the color yield.
Time control setting time is determined based on fiber heating time, heat penetration time, fiber macromolecule adjustment time and fabric cooling time. Generally, the setting temperature is high and the setting time is short. The setting time is also related to the maximum wind speed of the setting machine and the length of the oven. From the perspective of product quality, it is appropriate to use low temperature for a long time, but equipment and production efficiency must be taken into consideration.
If the above preforming temperature is selected, the preforming time is generally 20-30s. If the fabric thickness and moisture content increase, the time needs to be extended, which can be achieved by adjusting the speed of the shaping machine.
If the length of the setting machine is increased, the speed can be increased; the setting tension only needs to be able to achieve the flatness of the fabric. Just ensure the appearance requirements, so as not to affect the fullness and drape of the fabric, and overfeed appropriately in the warp direction to ensure warp buckling. </p
