Determination of polyester molding process
Polyester is a kind of thermoplastic fiber. In a series of dyeing and other processes, due to repeated mechanical action and stretching, the original gate width and coil geometry of the fabric have changed, resulting in deformation and shrinkage, and even skewed straight and straight silk, seriously affecting the quality of the product.
The main purpose of heat setting is to heat polyester knitted fabrics under tension and bake them at specified temperatures, which intensifies the thermal movement of secondary bonds and molecular chains between fibers, thus rearranging and arranging the molecules and making the internal stress relatively stable.
Therefore, it can improve the dimensional stability and wrinkle resistance of fabrics, as well as the surface finish, strength and pilling resistance of fabrics.
Control two points
The key to the heat setting process of polyester knitted fabric is to control the setting temperature and setting time.
If the heat setting temperature is too low and the time is too short, the fabric surface will be uneven, not stiff, shrinkage of the door width and other defects, lose the setting effect.
If the setting temperature is too high or the setting time is too long, the fabric will become rigid and brittle, the strength will decrease, the elasticity will decrease, and some disperse dyes will be sublimated to produce color difference, and even the fiber can be melted seriously.
Calculation formula of polyester molding time
Practice has proved that the suitable setting temperature of polyester knitted fabrics is 180-210 C, setting time is 20-90 s, and cooling temperature is about 50 C.
It can be calculated by pressing mode (according to different setting mechanisms):
Setting time (s) = setting length (m) / fabric linear velocity (m/min) × 60
When the setting temperature is 185-190 C, the linear speed of all kinds of polyester knitted fabrics is 10-15m/min for polyester warp knitted mosquito nets, 12-18m/min for polyester warp knitted shirts, 12-20m/min for polyester warp, weft and knitted jacquard fabrics, and 7-lOm/min for polyester dyed jacquard fabrics.
When setting, we should not neglect the proper coordination of the fabric's & ldquo; tension & rdquo; and & ldquo; overfeeding & rdquo.
If the width of the stretch exceeds the width of the fabric, the shrinkage rate will increase and the strength will decrease.
If the overfeeding is too large or the tension is not equal, it is easy to cause zonal wave (commonly known as & ldquo; agaric edge & rdquo); otherwise, it will produce stripes in the meridional direction. In short, in the operation process, we must strictly control the width, tension, over feeding and other process conditions.
Main purpose of predefined form
The crescent edges formed in the pretreatment process can be eliminated, the expansion changes in the subsequent processing can be stabilized, the uniformity of molecular structure arrangement in the amorphous region of polyester macromolecule can be improved, the crystallization defects can be reduced, the crystallinity can be increased, and the uniformity of alkali reduction can be improved.
The fabric of loose shrinkage is affected by the dry heat, and the style of printing and dyeing fabrics is affected. Because in order to eliminate wrinkles and improve the uniformity of molecular structure arrangement, tension must be exerted on the fabric, and the increase of strength will reduce the crepe effect, reduce the activity, and deteriorate a series of properties such as softness, resilience and fullness.
Attention point
Overfeeding shrinkage can compensate for the change of fabric style caused by increased tension during setting. Tension can reduce crepe effect, but can improve the uniformity of reduction and dimensional stability. To this end, relaxation should be avoided as much as possible during processing, so it is generally not dry before setting. If drying, pine drying equipment should also be used.
In order to avoid the disappearance of crepe effect and influence the fabric style, the width of setting is generally 4-5 cm smaller than that of finished products, or 2-3 CrN wider than that of pretreatment. The tension of front guide roll is relaxed, and proper overfeeding (such as increasing by 10%-20%) is added to maintain warp buckling and improve fabric style. The cooling system ensures normal operation to prevent pressure. Wrinkle, melt and harden.
temperature control
The predetermined temperature is generally controlled at: 180— 190:C. The setting temperature is low, which is beneficial to the fabric feel, but the damp heat wrinkle increases. The decrement rate and color yield vary with the change of setting temperature. The decrement rate and color yield decrease with the increase of temperature below 170-180 C. The decrement rate and color yield increase with the increase of temperature between 190-230 C. Therefore, the predetermined temperature should be selected according to the reduction rate and the fabric style requirement.
time control
The setting time is determined according to the heating time, thermal penetration time, 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 and the length of the oven. From the point of view of product quality, low temperature and long time should be considered, but equipment and production efficiency must be taken into account.
If the predetermined temperature is selected, the predetermined time is generally 20— 30s. If the thickness and moisture content of the fabric increase, the time will be prolonged. One can be achieved by adjusting the speed of the shaping locomotive.
If the length of the setting machine is increased, the speed of the car will be increased; the tension of the setting machine can only reach the fabric smoothness and ensure the appearance requirements, so as to avoid affecting the fabric fullness and drape, and the warp will be properly overfed to ensure warp buckling.