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 polyester knitted fabrics under tension and bake the fabrics at a specified temperature to make the secondary bonds between fiber molecules and molecular segments Thermal movement intensifies, which allows the molecules to recombine and arrange, and the internal stress is relatively stable.
This can improve the dimensional stability of the fabric, enhance the anti-wrinkle performance, and also improve the surface finish, strength, anti-pilling and other properties of the fabric.
Control two points
The key to the heat setting process of polyester knitted fabrics 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 uneven fabric surface, looseness, shrinkage of the width, etc., and lose the setting effect;
If the setting temperature is too high or the setting time is too long, it will cause the fabric to become hard and brittle, with reduced strength and elasticity. It can also cause some disperse dyes to sublime and cause color difference. In severe cases, it can even cause the fiber to melt. .
Polyester setting time calculation formula
Practice has proved that polyester knitted fabrics The suitable setting temperature is 180-210℃, the setting time is 20-90s, and the cooling temperature is about 50℃.
It can be calculated according to the following formula (calculated according to different shaping machine structures):
Setting time (s) = shaping length (m )/fabric linear speed (m/min) × 60
All kinds of polyester knitted fabrics are on the Z921 needle plate tenter setting machine. When the setting temperature is 185-190°C, The linear speed is: polyester warp knitted mosquito net cloth 10-15m/min, polyester warp knitted shirt cloth 12-18m/min, polyester warp, weft and knitted outerwear cloth 12-20m/min, polyester yarn-dyed jacquard cloth 7-10m/min. min.
When setting the shape, the “tension” and “overfeed” of the fabric should not be ignored and should cooperate appropriately with each other.
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 edges”), otherwise stripes will occur in the warp direction. In short, process conditions such as width, tension, and overfeeding must be strictly controlled during the operation.
Expansion of stereotyped knowledge
Main purpose of preforming
Eliminate the wrinkles produced during the pre-treatment process and some crescent edges formed during the relaxation and untwisting treatment, stabilize the expansion and contraction changes in subsequent processing, and improve the uniformity of the molecular structure arrangement in the amorphous region of polyester macromolecules , reduce crystal defects, increase crystallinity, and improve the uniformity of subsequent alkali reduction.
After the relaxed and shrunk fabrics are preformed 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.
Notes
This can be compensated by overfeeding and shrinkage during shaping. Changes in fabric style caused by increasing 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, and the front guide roller All tensions are relaxed, and appropriate overfeeding (such as increasing by 10% to 20%) is added 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
The setting time is based on the fiber heating time and heat penetration The time, fiber macromolecule adjustment time and fabric cooling time are determined. 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-mentioned pre-shaping temperature is selected, the pre-shaping 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