Fine denier yarn has broad application space in the field of knitting, and it can meet people’s increasing requirements for the texture of textile clothing. Due to the fineness of the fine denier yarn, various quality problems such as lint, tight twisting, and broken ends are prone to occur during processing, resulting in a low qualification rate for this type of product and an increase in production costs. In order to solve the above problems, this article successfully produced 44dtex/48f fine denier elastic yarn by optimizing the post-processing parameters and component materials and structures of nylon fine denier elastic yarn, and tested and characterized its various indicators, dyeing and appearance.
Test
1.1 Raw Materials
By this The various indicators of POY (specification 52dtex/48f) produced by the company are shown in Table 1.
1.2 Texturing and testing equipment
Texturing equipment: RPR 3SDY/2E, Italy.
Testing instruments: U STER evenness tester, Switzerland; FPA-M tensile tester, Germany.
1.3 Process flow
POY→first roller→hot box→cooling plate→false twisting Machine → Second roller → Oiling → Winding → DTY
1.4 Main process parameters and indicators
The main process parameter controls for post-spinning texturing are shown in Table 2.
The physical indicators of the processed DTY (specification: 44dtex/48f are shown in Table 3.
Results and discussion
2.1 Process parameters
2.1.1 Wire speed
Under normal production conditions, as the wire speed increases, the contact pressure between the wire and the friction disc increases, resulting in less slippage and false twisting. The effect is good. However, as the wire speed increases, the deformation and cooling time decrease, and the thermoplasticity of the wire decreases. If the wire speed is too high, tension fluctuations will occur, the wire operation will be unstable, and the number of untwisted wires will increase, so the wool will , the number of broken ends increases, resulting in poor fluffiness of the cheese yarn and a greatly reduced dyeing uniformity of the threads. Due to its small fineness, single fineness and high false twist, fine denier fibers should be used for this type of sensitive low-denier fibers. Relatively low wire speed. Through tests on the impact of different wire speeds on production (see Table 4), considering factors such as output and production stability, a wire speed of about 600m/min is appropriate.
Table 4 Comparison of processing conditions at different wire speeds
2.1.2 Stretch ratio
Stretch ratio It is generally determined by the residual draw ratio of POY, which directly affects the fineness, strength and elongation of the yarn. As the draw ratio increases, the strength of the yarn increases, the elongation decreases, the crimp rate is low, and the crimp stability improves. This The main reason is that as the draw ratio increases, the fiber macromolecules stretch and are neatly arranged along the fiber axis. The orientation of the drawn filament increases, and the crystallization of the macromolecules is induced, thereby increasing the strength of the filament. Because under high draw ratio, the orientation degree of macromolecules in the fiber increases, the possibility of further stretching decreases, so during the drawing process, the ability to be stretched again decreases; in addition, as the draw ratio increases, the tension High limits the rapid displacement required for the development of fiber curl, and the fiber curl is dense, so the curl rate is reduced and the curl stability is improved. If the draw ratio is too low, the tension will be small, easy to fluctuate, slip, and produce tight twists. Therefore, appropriately increasing the draw ratio within a certain range can stabilize the twisting, make the difference between spindle positions small, increase the A rate of dyeing, and reduce the difference in post-processing. For single fine fibers, the stretching cannot be too large, and the adjustable range is also relatively narrow. The effects of different draw ratios on fiber physical indicators are shown in Table 5. According to the elongation of the raw material of about 66%, the test shows that a stretch of about 1.255 is more suitable, and the tension is between 16-18cN.
2.1.3 Speed ratio
Speed ratio (D/Y ) is the key to determine the bulkiness, elasticity and feel of the processed yarn. The greater the degree of false twist, the greater the crimping force, the crimping will be thin and more, and the appearance of the filament will be plumper after untwisting, and because the twisting absorbs the tension fluctuation caused by stretching at the same time, the tension change will be reduced. , the wire deformation is uniform and good. The effects of different speed ratios on various fiber indicators are shown in Table 6. If the D/Y ratio is too high, it is easy to cause uneven fiber twist and slippage, and as the frictional resistance increases, the strength of the filament will decrease, and the wool will decrease. There are too many filaments; the D/Y ratio is too low, which can easily cause tension fluctuations, poor false twisting effect, and uniform dyeing. The optimal D/Y ratio is determined by the positive pressure of the thread acting on the disc and the friction coefficient between the thread and the dial. Generally, the ratio of untwisting tension and twisting tension is 1. The elasticity index of DTY processing must be appropriately adjusted according to customer requirements. Since this product is mainly used for weaving, the elasticity needs to be appropriately reduced, so the speed ratio is 1.6.
2.1.4 Hot box temperature
The temperature of the hot box mainly affects the curl elongation, color fastness and dyeability of the filament. The effects of different temperatures on various fiber indicators are shown in Table 7. At lower temperatures, as the temperature increases, the mobility of molecules gradually increases, and the internal stress generated by thermal deformation decreases, thereby fully deforming the plastic reinforced fibers of the filament, improving the fluffiness, and increasing the strength of the filament. . However, as the temperature further increases, the amorphous orientation within the fiber is prone to de-orientation, making the fiber brittle and thus reducing strength. It is also prone to bonding between wool filaments or single filaments, resulting in stiff filaments and greatly reducing the crimp of the filaments. sex. When the temperature is too low, the deformation of the filament is insufficient, resulting in a reduction in the curling rate and curl stability, and the filament is soft and inelastic and becomes cotton filament. When processing fine denier yarn, due to the fine fiber fineness and large specific surface area, contact with the hot box and improved heating performance, a slightly lower temperature can be selected, and combined with a production speed of 600 m/min, 175°C is appropriate.
2.2 Equipment and components
2.2.1 Model
When processing fine-denier elastic yarn, due to the low fiber fineness and high twist requirements, if the twist resistance tension of the filament is too large during the processing, it will easily lead to increased breakage. Therefore, a V-shaped machine with relatively small resistance on the wire should be used (the hot box and the cooling plate are in a straight line). Since the twisting area of this model is relatively short, the effectiveness of twisting is improved; and there is less static electricity during processing, which reduces the tension fluctuation of the filament in the twisting area, improves the stability of the filament, and improves the product qualification rate.
2.2.2 Twist resistor
Twister resistors are made of ceramic and metal. The metal twist resistor is easy to deform during use, so it is easy to produce tight twists or even stiff wires after being used for a period of time. When processing 44dtex/48f fine denier yarn, due to the small fineness of the fiber, in order to ensure the twisting degree of the filament, the twist resistance effect of the twist resistor is relatively high. Therefore, non-deformable ceramic twist resistors are generally used. Due to their consistent twist resistance effect, they can ensure consistent and uniform twisting of the filament in the twisting area, thus improving the internal quality of the elastic yarn and improving the A color rate of the filament. Stable product quality.
2.2.3 Friction disc
Friction discs are mainly divided into two types according to material: ceramic and polyurethane. . Friction discs can be divided into three types according to the combination: introduction disc, working disc and lead-out disc. Among them, the lead-in disc has the largest force, and ceramic discs are generally used; the lead-out disc is made into a knife-edge shape to eliminate tight spots, and ceramic or metal discs are generally used; for processing For fine denier yarns with low fineness and large single fiber contact area, it is best to use polyurethane disks for the working disk, because polyurethane disks made of elastomer materials have better false twisting effects, are less likely to slip, and produce less snowflakes than ceramic disks made of hard materials. Other advantages can greatly improve the strength of the thread. However, the service life of polyurethane disks is short, generally about 6 months.
2.2.4 Others
The 44dtex/48f specification fiber has low fineness and single fineness. Processed components have higher requirements. First, install a thread guide at the first roller to make the yarn go around the FR1 pressure roller (same as FR2) to ensure stable holding points at both ends, thereby reducing light leakage and deviation from the pressure roller. The changes in tensile tension caused by this can reduce the occurrence of tight twists and differences between spindle positions, thereby stabilizing production and improving product quality.
Secondly, the yarn guide in the false twist area should be smooth and the friction coefficient should be small. In this way, during the production process, the contact area between the yarn and the yarn guide is small and the resistance is small. The wear on the yarn is small, thereby improving the strength of the yarn and dyeing uniformity.
Finally, due to the large specific surface area of 44dtex/48f fine denier yarn and poor relative cohesion, if the oil content is low, the yarn will be loose and easy to break during post-processing, so it should be Increase the oil content appropriately. However, the wrapping angle between the wire and the tanker cannot be too large, otherwise the resistance generated will be relatively large, which may easily lead to breakage of the floating wire. However, the oil content of the fiber cannot be too high, otherwise it will easily lead to large oil stains during post-processing and difficulty in cleaning. The empirical value is an oil content of about 3%.
Conclusion
(1) The best process for processing 44dtex/48f nylon fine denier elastic yarn The conditions are: wire speed 600m/min, draw ratio 1.255, speed ratio 1.6, and temperature 175°C. Physical indicators of elastic yarn: strength 3.71cN/dtex. The elongation is 20.8%, the curl rate is 38.9%, and the curl stability is 48.7%.
(2) When processing fine-denier elastic yarn, ceramic twist resistors and polyurethane friction discs should be selected to ensure consistent and stable elasticity of the elastic yarn and improve the strength of the yarn.
(3) When processing fine denier yarn, it is necessary to carefully analyze and compare the yarn from the yarn rack to winding the entire post-spinning yarn, and optimize the selection to improve product quality and reduce production. cost. </p
