Method for improving flexibility of polyester fibers

Abstract

The invention belongs to the technical field of textile, and relates to a method for improving the flexibility of polyester fibers. According to the method, in the PET melt spinning process, 0.3 wt%-0.9 wt% of hydroxyl-terminated polydimethylsiloxane is introduced into a PET melt in a master batch form; the master batch is composed of a carrier PET and silicone, the silicone content in the master batch is 30 wt% + / -5 wt%, and the intrinsic viscosity of the PET and the carrier in the master batch is 1.12 dL / g; the technological process of PET melt spinning comprises the steps of melt extrusion of a double-screw extruder, side blowing cooling, oiling, drafting of a three-stage drafting hot roller and winding, wherein the rotating speed of screws of the double-screw extruder is controlled to be 30 r / min. The flexibility of the polyester fiber is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of textile technology and relates to a method for improving the flexibility of polyester fibers; this invention is a divisional application with application number 2025118556602, application date December 10, 2025, entitled "Method for reducing PET melt spinning pressure with low damage to fiber properties". Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in industrial yarn applications such as tire cord fabric, geotextiles, and airbags due to its high strength, chemical resistance, and low cost. These applications place extremely high demands on the mechanical properties and dimensional stability of the fibers. However, high molecular weight PET melt exhibits high viscosity during melt spinning, leading to a significant increase in the pressure of the spinning assembly. This not only limits spinning speed and production line efficiency but also easily causes problems such as spinneret blockage, affecting production stability.

[0003] To improve the melt flowability of PET and reduce spinning pressure, various methods have been developed in the existing technology.

[0004] Temperature control is a commonly used adjustment method in industry. By increasing the spinning temperature (e.g., from 280℃ to 300℃), the apparent viscosity of the melt is reduced to achieve pressure reduction. However, it has significant drawbacks: excessively high processing temperatures will accelerate the thermal degradation of PET, leading to molecular chain breakage, decrease in intrinsic viscosity, and yellowing, which directly damages the mechanical properties and thermal stability of the fiber. At the same time, it greatly increases energy consumption and is not conducive to energy-saving and carbon-reducing production.

[0005] Chemical copolymerization modification improves molecular chain flexibility and reduces melt viscosity by introducing flexible comonomers such as polyethylene glycol, triethylene glycol, and isophthalic acid into the PET backbone (e.g., patent US6890524B2). However, this method alters the PET molecular backbone structure, leading to a decrease in polymer crystallinity and melting point (typically by 10-20°C), limiting its application under high-strength or high-temperature conditions. Furthermore, the choice of comonomers is limited, the synthesis process is complex, and batch-to-batch product stability is poor, making it difficult to meet the performance consistency requirements of industrial yarns.

[0006] Nanofillers or inorganic modification methods introduce nano-montmorillonite, nano-silica, alumina, or surface-modified polytetrafluoroethylene (PTFE) nanoparticles (such as patent CN113430658B) to reduce flow resistance by utilizing the particle's ability to regulate the rheological properties of the melt. However, such methods rely on the uniform dispersion of solid particles, while nanoparticles are prone to agglomeration. This not only makes it difficult to stably reduce spinning pressure but also leads to decreased spinning stability and an increased risk of spinneret blockage. At the same time, the poor compatibility between the particles and the PET matrix can easily cause problems such as fiber breakage and uneven thickness, and even indirectly affect the mechanical properties of the fiber. As CN113430658B also points out, although reducing the molecular weight or adding small molecule flow promoters can reduce pressure, it will significantly reduce the mechanical properties of industrial yarns.

[0007] Equipment structure improvement methods improve the melt flow field distribution and reduce local resistance by optimizing the spinneret orifice diameter, screw compression ratio, or coating the screw surface with a molybdenum disulfide lubricating layer (such as patent application CN112342879A). However, such solutions have equipment maintenance challenges. For example, the lubricating coating is prone to wear and failure under high temperature and high shear conditions, requiring frequent shutdowns for replacement. This not only affects production efficiency but may also cause the coating to peel off and contaminate the melt, thereby damaging fiber quality.

[0008] In summary, existing technologies cannot meet the dual requirements of "low spinning pressure" and "high fiber performance" in industrial yarn production. Summary of the Invention

[0009] The purpose of this invention is to solve the problems existing in the prior art and to provide a method for reducing PET melt spinning pressure with low damage to fiber properties.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for reducing PET melt spinning pressure with low damage to fiber properties involves introducing 0.6wt%-1.2wt% silicone into the PET melt.

[0012] The silicone is a hydroxyl-terminated polydimethylsiloxane (structural formula: The number average molecular weight of silicone is 5000-30000 g / mol. Silicone is added in the form of masterbatch, which consists of carrier PET and silicone. The silicone content in the masterbatch is 30wt%±5wt%.

[0013] This invention adds masterbatch to PET, allowing silicone molecules to enter the long chains of PET molecules during the melting stage. The silicone molecules form a molecular-level lubricating layer between the PET molecular chains, reducing inter-chain entanglement and internal friction through their low-friction properties. This significantly reduces melt viscosity and spinning assembly pressure without altering the PET main chain structure, while maintaining bulk intrinsic viscosity and fiber mechanical properties as much as possible. This method does not require changing the bulk molecular weight of PET and does not rely on nanoparticle dispersion, making it suitable for existing industrial spinning production lines with good process compatibility and stable operation. Specifically, the ability of this invention to quantitatively reduce spinning assembly pressure while ensuring minimal damage to fiber properties is mainly attributed to the following aspects:

[0014] (1) Silicone is added in the form of masterbatch: The purpose is to ensure the uniform distribution of silicone in the solid feed and melt extrusion stages and to achieve controlled release, avoiding phase separation, bubbles or agglomeration caused by direct addition of liquid / powder. During the spinning process, the masterbatch gradually melts in the melt, and silicone molecules are stably and slowly diffused and released from the carrier, and migrate uniformly along the melt flow direction. When the melt passes through high shear and high pressure drop areas (such as metering pumps, distribution and spinneret components), silicone molecules form a molecular-level lubricating layer between the inner wall of the spinning component and the melt. This lubricating layer can significantly reduce the interfacial friction coefficient, weaken the adhesion and dragging effect between the polyester melt and the metal channel, thereby reducing the overall pressure of the spinning component by about 5%-17%. Since the silicone is released in the form of masterbatch, its distribution in the flow field is stable and will not have a significant impact on the molecular weight, crystallization behavior and orientation of the polyester body. Therefore, the strength, elongation at break and initial modulus of the fiber during the stretching and setting process remain above 95% of the original system, achieving both pressure reduction and performance.

[0015] (2) Control of silicone content in masterbatch: Ensure that sufficient silicone can be released in a short time to form a lubricating film at the specified addition amount. If the content is too low, the release is more uniform but the release amount of each masterbatch is small. The instantaneous supply at the interface may not be enough to form a continuous film in the high shear zone and can only play a local lubricating role. At this time, there is still significant frictional resistance between the melt and the metal interface, resulting in a limited pressure drop of the component (usually less than 5%). The fiber is subjected to uneven force in the flow field, and some areas experience shear heating and molecular orientation too fast, which leads to uneven fiber crystallization and a decrease in breaking elongation. If the content is too high, the instantaneous amount of silicone released by a single masterbatch is large, but the number of masterbatches is small, and the release may be uneven. Local interfaces may be oversaturated while other areas are insufficient. The short-term effect is strong but the sustainability is poor. This uneven lubrication state will cause the melt pressure to drop significantly in a short time, but the sustainability is poor. At the same time, the local enrichment of silicone will migrate to the fiber surface to form a film, which will inhibit the fiber surface orientation and slip during stretching, resulting in a decrease in breaking strength, increased fuzz and adhesion.

[0016] (3) Control of silicone content in melt: The feed produces a suitable total silicone concentration to form a stable but not too thick lubricating layer. Too low → pressure drop is not obvious; too high → fiber surface is too slippery, stretching is unstable and mechanical properties decrease.

[0017] (4) Chemical structure of silicone - hydroxyl end-capping: Hydroxyl end-capping improves the compatibility of silicone with the PET matrix, which facilitates masterbatch preparation and orderly migration at high temperatures, forming a stable layer at the interface. This moderate compatibility allows silicone molecules to migrate orderly to the metal wall during flow and form a lubricating layer on the wall. This lubricating layer can significantly reduce interfacial shear stress, thereby stabilizing and reducing system pressure. Non-hydroxyl or completely inert end groups may reduce compatibility or migration; improper reactivity may cause side reactions, crosslinking or degradation, and layering or microphase separation may easily occur in the melt. Uneven local lubrication leads to increased pressure fluctuations and unstable spinning.

[0018] (5) The molecular weight of silicone is controlled within the range of 5000-30000 g / mol: Molecular weight affects migration rate, volatility, and lubricating film stability. Medium molecular weight silicone can migrate without being easily volatilized or lost. It has sufficient fluidity to migrate and form a lubricating layer, as well as sufficient thermal stability and intramolecular forces to maintain the thickness and integrity of the lubricating layer. Silicone in this molecular weight range can significantly reduce component pressure. At the same time, since silicone hardly participates in chemical reactions within this range, its existence is stable and has minimal impact on the crystallinity and orientation of PET. Therefore, the mechanical properties of the fiber are maintained well.

[0019] The method described above for reducing PET melt spinning pressure with low damage to fiber properties has a silicone number-average molecular weight of 10,000 g / mol and a silicone content of 30 wt% in the masterbatch.

[0020] As a preferred technical solution:

[0021] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties has an intrinsic viscosity of PET (tested according to standard GB / T14190-2008 "Test Methods for Fiber Grade Polyester Chips (PET)") of 1.13 dL / g. The intrinsic viscosity of the carrier in the masterbatch is the same as that of the PET. The purpose is to reduce the error in measuring the intrinsic viscosity of the subsequent oil-free yarn (referring to the initial spinning yarn without oiling agent). If the intrinsic viscosity of the carrier is high or low, it will affect the viscosity reduction of the subsequent oil-free yarn.

[0022] As described above, a method for reducing PET melt spinning pressure with minimal damage to fiber properties involves introducing silicone into the PET melt by mixing PET chips with masterbatch, followed by drying (to avoid moisture-induced thermal degradation that could affect silicone behavior and fiber properties) and melt blending.

[0023] The above-described method for reducing PET melt spinning pressure with minimal damage to fiber properties involves vacuum drying at a temperature of 160-175°C for 8 hours. After drying, the moisture content of both the PET chips and the masterbatch is less than 50 ppm.

[0024] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties involves drying at a temperature of 170°C, resulting in a moisture content of 35 ppm for both the PET chips and the masterbatch after drying.

[0025] As described above, a method for reducing PET melt spinning pressure with minimal damage to fiber properties involves dehumidifying and drying both PET chips and masterbatch before mixing. The dehumidification and drying process is carried out at a temperature of 160-175°C for 6-10 hours.

[0026] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties involves a dehumidification drying process at a temperature of 170°C for 8 hours.

[0027] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties involves a surface energy of 35-55 mN / m and a roughness Ra of 0.05-0.25 μm for the spinneret assembly and its internal metal flow channel walls. The surfaces (specifically referring to the surfaces of the spinneret assembly and its internal metal flow channels, including the inner wall of the distributor channel, the inlet surface of the spinneret orifice, and the metal surface of the metering pump outlet transition section) are kept clean and free of oil or oxide layers. This ensures that silicone forms a continuous and stable molecular-level lubricating layer on the wall surface, thereby achieving a stable decrease in spinneret pressure while maintaining fiber properties.

[0028] The method described above for reducing PET melt spinning pressure with low damage to fiber properties has a surface energy of 45 mN / m and a roughness Ra of 0.2 μm for the spinneret and its internal metal flow channel inner wall.

[0029] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties includes the following process flow: twin-screw extruder melt extrusion → side-blowing cooling → oiling → winding → drafting machine (parallel drafting machine) drafting.

[0030] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties includes the following process parameters: a twin-screw extruder screw speed of 25 r / min, a twin-screw extruder melt section temperature of 290-305℃, and reasonable twin-screw extruder parameter settings that allow the silicone component in the masterbatch to be uniformly released in the melt and form a stable lubricating layer without significantly damaging fiber properties; a spinning temperature of 305℃ (same as existing technology); 36 spinneret orifices; 0.5 mm diameter spinneret orifices (circular); a winding speed of 800 m / min; a drafting machine hot plate temperature of 80℃; a drafting machine hot plate temperature of 160℃; and a draft ratio of 3.5-4.0 times.

[0031] The method described above for reducing PET melt spinning pressure with minimal damage to fiber properties involves a twin-screw extruder with a melt section temperature of 300°C and a draw ratio of 3.8.

[0032] The method described above for reducing PET melt spinning pressure with low damage to fiber properties reduces the pressure of the spinning assembly by 5.7%-17% during the PET melt spinning process compared to the comparative production line. The intrinsic viscosity of the intermediate product oil-free filament of PET melt spinning decreases by ≤0.03dL / g, and the breaking strength of the final product PET fiber of PET melt spinning decreases by no more than 10%. The comparative production line is a production line that produces PET using the same process but does not introduce silicone into the PET melt.

[0033] The final product of PET melt spinning, PET fiber, has a breaking strength of 5.5-5.9 cN / dtex and a breaking elongation of 9.6%-10.3%.

[0034] Keeping other conditions unchanged, adjusting the intrinsic viscosity of PET from 1.13 dL / g to 1.12 dL / g, adjusting the screw speed of the twin-screw extruder from 25 r / min to 30 r / min, and adjusting the spinning temperature from 305℃ to 290-295℃ (a reduction of 10-15℃ compared to existing technologies) can achieve the effect of improving fiber mechanical properties while reducing the PET melt spinning temperature. This is because the addition of silicone can reduce the melt viscosity, thereby allowing the spinning temperature to drop by 10-15℃, thus mitigating the degradation of PET melt during spinning and improving fiber mechanical properties (specifically, the breaking strength of the final PET melt-spun product, PET fiber, increases from 5.5-5.9 cN / dtex to 6.03-6.26 cN / dtex; in particular, when the silicone content in the melt is 0.6 wt%, the breaking strength of the final PET melt-spun product, PET fiber, increases from 6.13 cN / dtex to 6.26 cN / dtex). In addition, the present invention reduces the intrinsic viscosity of PET and increases the screw speed of the twin-screw extruder. Because reducing the intrinsic viscosity of PET and increasing the screw speed can work synergistically to promote the formation of a more uniform molecular orientation structure, thereby reducing thermal degradation, improving grain uniformity, and ultimately improving the fiber's breaking strength, initial modulus stability and elongation at break, which is beneficial to improving the fiber's mechanical properties.

[0035] Studies have shown that in order to improve the mechanical properties of fibers while lowering the melt spinning temperature of PET, in addition to adjusting the intrinsic viscosity of PET, the screw speed of the twin-screw extruder, and the spinning temperature, other necessary conditions must be met, and the reasons are as follows:

[0036] (1) Silicone must be added to PET in masterbatch form, rather than directly adding liquid or powdered silicone;

[0037] Adding silicone in masterbatch form ensures uniform dispersion of silicone during solid-phase mixing and melt extrusion, and allows for stable and controllable release during the melting stage. This enables silicone molecules to migrate orderly to inter-chain spaces and metal walls during melt flow, forming a continuous molecular-level lubricating layer. This lubricating layer significantly reduces melt viscosity and interfacial shear friction, thereby achieving stable spinning under low-temperature conditions.

[0038] Directly adding liquid or powdered silicone will lead to silicone phase separation, localized enrichment, bubble generation, or discontinuous lubrication, resulting in increased melt pressure fluctuations, unstable fiber drawing, and a decline in fiber performance. Therefore, using masterbatch is a necessary condition for realizing the technical solution of this invention.

[0039] (2) The content of silicone in the masterbatch needs to be controlled at 30wt%±5wt%;

[0040] When the silicone content in the masterbatch is 30wt%±5wt%, the release amount of a single masterbatch is sufficient and the number of masterbatches is moderate, so that the silicone can be continuously released in the melt and maintain a high spatial uniformity, ensuring that the interfacial lubricating film is stably formed in the spinneret assembly.

[0041] If the silicone content is too low, it will be difficult to provide enough silicone to form a stable lubricating layer in a short time, resulting in a weak cooling effect; if the content is too high, the number of masterbatches will decrease, the release will be uneven, and local enrichment will easily occur, thereby aggravating melt pressure fluctuations and causing fiber surface slippage or a decrease in strength. Therefore, controlling the silicone content in the masterbatch is a necessary condition for achieving stable cooling and performance maintenance in this invention.

[0042] (3) The total amount of silicone added to the melt should be controlled between 0.6wt% and 1.2wt%;

[0043] Research has shown that when the amount of silicone added is 0.6wt%, PET crystallization temperature is the highest, the half-peak width of the crystallization peak is the smallest, and the crystallinity is the largest. This indicates that the chain segment regularity and nucleation ability are optimal, which can form a higher degree of orientation and a more uniform crystal structure during the drawing process, so that the fiber strength reaches the optimal level. At the same time, due to the significant lubrication effect, the spinning temperature can be reduced by 10-15℃ and the component pressure can be significantly reduced.

[0044] If the addition amount is less than 0.6 wt%, the silicone is insufficient to form a continuous lubricating film, resulting in a weak cooling effect; if it exceeds 1.2 wt%, a large amount of silicone migrates to the fiber surface, leading to draft slippage, reduced surface orientation, and decreased strength. Therefore, this addition range is a necessary condition for achieving both low temperature and high strength in this invention.

[0045] (4) Silicone must have a hydroxyl-terminated structure;

[0046] The hydroxyl-terminated structure provides moderate compatibility between silicone and PET, preventing melt phase separation and ensuring uniform distribution of silicone in the melt. It also promotes the migration of silicone molecules along the flow field to the metal wall to form a stable lubricating layer.

[0047] If completely inert end groups (such as methyl end-caps) are used, poor compatibility leads to silicone phase separation, preventing the continuous formation of the lubricating film. If reactive end groups are used, transesterification or cross-linking reactions may be initiated, resulting in abnormal fluctuations in melt viscosity. Therefore, hydroxyl-terminated silicone is a necessary condition for forming a stable lubricating layer and maintaining the PET backbone structure without damage.

[0048] (5) The molecular weight of silicone needs to be controlled within a medium range (number average molecular weight of 5000-30000 g / mol).

[0049] Medium molecular weight silicones have moderate migration and thermal stability, allowing them to migrate to metal walls at melt spinning temperatures to form a stable lubricating layer. They are also less prone to volatilization or migration is hindered by excessively large molecular weights.

[0050] If the molecular weight of the silicone is too low, it migrates too quickly, causing excessive lubrication of the fiber surface, hindering orientation, and leading to a decrease in strength. If the molecular weight of the silicone is too high, its migration ability is insufficient, the lubricating film cannot be formed, and it is difficult to reduce the spinning temperature. Therefore, controlling the molecular weight range is a necessary condition for achieving stable lubrication and good fiber properties in this invention.

[0051] Alternatively, keeping other conditions unchanged, adjusting the silicone content in the PET melt from 0.6wt%-1.2wt% to 0.3wt%-0.9wt%, the intrinsic viscosity of PET from 1.13dL / g to 1.12dL / g, the screw speed of the twin-screw extruder from 25r / min to 30r / min, and changing the PET melt spinning process from spinning followed by drawing to continuous spinning and drawing (the PET melt spinning process includes: twin-screw extruder melt extrusion → side-blown cooling → oiling → three-stage drawing hot roller drawing → winding) can significantly improve the flexibility of PET fibers for the following reasons:

[0052] Controlling the silicone content in the melt to 0.3wt%-0.9wt% can form a molecular-level lubricating layer between PET chain segments and improve the degree of freedom of chain segment movement. This results in increased fiber elongation at break and a moderate decrease in initial modulus (specifically, the initial modulus of the final PET melt-spun product, PET fiber, decreases from 65-70 cN / dtex to 48-58 cN / dtex compared to the comparative production line, while the elongation at break increases from 18%-22% to 23%-30%. The comparative production line is a line using the same process but without introducing silicone into the PET melt). This leads to better bending properties and fatigue resistance. If the silicone content is too low, lubrication / softening is insufficient, limiting the improvement in chain segment freedom of movement; if the silicone content is too high, a large amount of silicone migrates to the fiber surface, causing stretching slippage, resulting in decreased strength and excessive reduction in initial modulus.

[0053] Controlling the intrinsic viscosity of PET to 1.12 dL / g allows the polyester molecular chain to have appropriate fluidity and chain segment mobility, which is conducive to the more uniform dispersion of silicone in the melt and to give full play to the inter-chain lubrication and softening effect, thereby improving the fiber's elongation at break and improving its flexibility.

[0054] Controlling the screw speed of the twin-screw extruder to 30 r / min can enhance the mixing effect and shear dispersion of the melt, making the silicone additives more evenly distributed in the melt. This helps to form a fine and uniform grain structure during fiber forming, thereby improving the bending durability and flexibility of the fiber.

[0055] Controlling the continuous spinning and drawing processes during PET melt spinning is beneficial for moderate molecular chain orientation, moderate crystallinity, and improved chain segment freedom of movement, which is essential for flexibility.

[0056] Studies have shown that in order to significantly improve the flexibility of PET fibers, in addition to adjusting the silicone content in the PET melt, the intrinsic viscosity of PET, the screw speed of the twin-screw extruder, and the PET melt spinning process, other necessary conditions must be met, and the reasons are as follows:

[0057] (1) Silicone must be added in the form of masterbatch, rather than directly adding liquid or powdered silicone;

[0058] The masterbatch ensures the uniform dispersion of silicone in the solid-phase mixing and melting stages of PET; during the melting process, silicone can be released stably and controllably, and migrate along the flow field to form a uniform lubricating layer and chain segment softening layer; it ensures that silicone is inserted into the chain at the molecular level, improves the freedom of chain segment movement, and significantly enhances the flexibility of the fiber.

[0059] Adding liquid or powdered silicone directly will lead to phase separation, local enrichment, discontinuous lubrication, increased slippage or breakage during the drawing process, and a decrease in fiber strength and flexibility.

[0060] (2) The content of silicone in the masterbatch needs to be controlled at 30wt%±5wt%;

[0061] A concentration of 30wt% ± 5wt% achieves an optimal balance between single-particle release, masterbatch quantity, and dispersion; it forms a well-covering inter-chain softening layer and interface lubrication layer during the melting stage; it facilitates grain refinement and maintains uniform fiber orientation, thereby improving flexibility and preserving strength. If the content is too low, insufficient silicone release will fail to significantly soften the chain segments; if the content is too high, uneven release will lead to excessive lubrication of the fiber surface and reduced orientation.

[0062] (3) Silicone must have a hydroxyl-terminated structure;

[0063] Hydroxyl end groups improve compatibility with PET and prevent phase separation; hydroxyl-free silicones cannot effectively form a lubricating layer; a stable thin layer can be formed at the melt interface to achieve chain segment softening.

[0064] Beneficial effects:

[0065] (1) This invention introduces silicone with a specific content, structure and molecular weight into the PET melt in the form of masterbatch. Without changing the PET main chain structure, without changing the molecular weight of PET, and without relying on nanoparticle dispersion, it can significantly reduce the pressure of the spinning assembly and maintain the intrinsic viscosity and fiber mechanical properties of PET as much as possible.

[0066] (2) The process of the present invention is simple to operate, does not require major modifications to existing industrial spinning production lines, has good process compatibility and stable operation. Attached Figure Description

[0067] Figure 1 The pressure changes during the spinning process of Examples A1-A3, the comparative production line of Example A1, and Comparative Example A2 are shown.

[0068] Figure 2 The melt-spinning process of Example A1;

[0069] Figure 3 The melt spinning process of Example C1 (GR1~GR3 in the figure correspond to the first hot roller, the second hot roller, and the third hot roller, respectively).

[0070] Among them, 1-hopper, 2-twin-screw extruder, 3-metering pump, 4-spinning assembly, 5-bundling device, 6-guide disc, 7-winding device, 8-three-stage drawing hot roller. Detailed Implementation

[0071] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0072] To ensure that the performance of the substances used in each embodiment and comparative example is fully disclosed, the manufacturer information of the substances is specified in this invention; in addition, products from other manufacturers that conform to the limitations of this invention are also applicable.

[0073] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0074] Moisture content: The moisture content of the sample was tested in accordance with GB / T 12006.4-1989 "Determination of moisture content of plastics - Part 4: Karl Fischer method". The Karl Fischer electrophoresis moisture analyzer was used, the test temperature was 150℃, and the sample was heated to the constant charge endpoint under nitrogen protection. The moisture content of the sample was controlled below 50ppm.

[0075] Intrinsic viscosity: Tested according to standard GB / T14190-2008; the thoroughly dried sample was dissolved in a mixed solvent of phenol and tetrachloroethane (mass ratio 1:1) to prepare a solution with a concentration of 0.50 g / dL. The intrinsic viscosity was measured in a constant temperature water bath at 25℃±0.05℃ using an Ubbelohde viscometer with a capillary diameter of 0.5~0.6 mm; the relevant calculation formula is as follows:

[0076] ;

[0077] ;

[0078] In the formula, Intrinsic viscosity (dL / g) To increase specific viscosity; The solution outflow time (s); Solvent outflow time (s); The concentration is the solution concentration (g / dL).

[0079] Initial modulus, breaking strength, and breaking elongation: The tests were conducted according to the test conditions of GB / T 14344-2008, using a YG020B single yarn strength tester. The test conditions were: temperature 20±2℃, relative humidity 65±5%, clamping distance 200mm, and tensile speed 200mm / min. Ten parallel tests were performed and the average value was taken.

[0080] Example A1

[0081] A method for reducing PET melt spinning pressure with minimal damage to fiber properties includes the following steps:

[0082] (1) Preparation of materials;

[0083] PET chips: intrinsic viscosity is 1.13 dL / g;

[0084] Masterbatch: Prepared by granulation of carrier PET and hydroxyl-terminated polydimethylsiloxane; the intrinsic viscosity of carrier PET is 1.13 dL / g; the manufacturer of hydroxyl-terminated polydimethylsiloxane is Jinan Longcheng Organosilicon Co., Ltd., with a number average molecular weight of 10000 g / mol; the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch is 30 wt%.

[0085] (2) The PET chips and masterbatch are successively dehumidified and dried, mixed and vacuum dried to obtain a mixture; wherein the dehumidification and drying temperature is 170℃ and the time is 8h; the vacuum drying temperature is 170℃.

[0086] After vacuum drying, the moisture content of both the PET chips and the masterbatch was 35 ppm; the content of hydroxyl-terminated polydimethylsiloxane in the mixture was 0.6 wt%.

[0087] (3) Melt spinning the mixture;

[0088] like Figure 2As shown, the process flow is as follows: feeding from hopper 1 → melt extrusion from twin-screw extruder 2 → conveying melt from metering pump 3 → extruding filaments from spinning assembly 4 → side-blowing cooling → oiling and bundling from bundling device 5 → guiding from guide disc 6 → winding from winding device 7 → drawing from drawing machine; wherein, the surface energy of the spinneret and its internal metal flow channel inner wall is 45mN / m, the roughness Ra is 0.2μm, and the surface is kept clean and free of oil or oxide layer;

[0089] The relevant process parameters are as follows: screw speed of twin-screw extruder 25 r / min, melt section temperature of twin-screw extruder 300℃, conveying section temperature of twin-screw extruder 310℃, spinning temperature 305℃, spinneret orifice number 36, spinneret orifice diameter 0.5 mm, winding speed 800 m / min, hot plate temperature of drawing mill 80℃, hot plate temperature of drawing mill 160℃, and draw ratio 3.8 times.

[0090] Tests show that, compared to the comparative production line, the pressure of the spinning component is reduced by 5.7% during melt spinning, the intrinsic viscosity of the intermediate product oil-free filament decreases by 0.01 dL / g, and the breaking strength of the final product PET fiber decreases by 3.28%. The only difference between the comparative production line and this embodiment is that no masterbatch is added.

[0091] The intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.88 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 5.9 cN / dtex, and the elongation at break is 9.6%.

[0092] Example A2

[0093] A method for reducing PET melt spinning pressure with minimal damage to fiber properties includes the following steps:

[0094] (1) Preparation of materials;

[0095] PET chips: intrinsic viscosity is 1.13 dL / g;

[0096] Masterbatch: Prepared by granulation of carrier PET and hydroxyl-terminated polydimethylsiloxane; the intrinsic viscosity of carrier PET is 1.13 dL / g; the manufacturer of hydroxyl-terminated polydimethylsiloxane is Jinan Longcheng Organosilicon Co., Ltd., with a number average molecular weight of 10000 g / mol; the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch is 30 wt%.

[0097] (2) The PET chips and masterbatch are successively dehumidified and dried, mixed and vacuum dried to obtain a mixture; wherein the dehumidification and drying temperature is 170℃ and the time is 8h; the vacuum drying temperature is 170℃.

[0098] After vacuum drying, the moisture content of both the PET chips and the masterbatch was 35 ppm; the content of hydroxyl-terminated polydimethylsiloxane in the mixture was 0.9 wt%.

[0099] (3) Melt spinning the mixture;

[0100] The process flow is as follows: feeding from the hopper → melt extrusion by a twin-screw extruder → conveying the melt by a metering pump → extruding filaments by the spinning assembly → side-blowing cooling → oiling and bundling by the bundling device → guiding by the guide disc → winding by the winding device → drawing by the drawing machine; wherein, the surface energy of the spinneret and its internal metal flow channel inner wall is 45mN / m, the roughness Ra is 0.2μm, and the surface is kept clean and free of oil or oxide layer;

[0101] The relevant process parameters are as follows: screw speed of twin-screw extruder 25 r / min, melt section temperature of twin-screw extruder 300℃, conveying section temperature of twin-screw extruder 310℃, spinning temperature 305℃, spinneret orifice number 36, spinneret orifice diameter 0.5 mm, winding speed 800 m / min, hot plate temperature of drawing mill 80℃, hot plate temperature of drawing mill 160℃, and draw ratio 3.8 times.

[0102] Tests show that, compared to the comparative production line, the pressure of the spinning component is reduced by 13.2% during melt spinning, the intrinsic viscosity of the intermediate product oil-free filament decreases by 0.02 dL / g, and the breaking strength of the final product PET fiber decreases by 6.56%. The only difference between the comparative production line and this embodiment is that no masterbatch is added.

[0103] The intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.87 dL / g; the tensile strength of the melt-spun final product, PET fiber, is 5.7 cN / dtex, and the elongation at break is 9.8%.

[0104] Example A3

[0105] A method for reducing PET melt spinning pressure with minimal damage to fiber properties includes the following steps:

[0106] (1) Preparation of materials;

[0107] PET chips: intrinsic viscosity is 1.13 dL / g;

[0108] Masterbatch: Prepared by granulation of carrier PET and hydroxyl-terminated polydimethylsiloxane; the intrinsic viscosity of carrier PET is 1.13 dL / g; the manufacturer of hydroxyl-terminated polydimethylsiloxane is Jinan Longcheng Organosilicon Co., Ltd., with a number average molecular weight of 10000 g / mol; the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch is 30 wt%.

[0109] (2) The PET chips and masterbatch are successively dehumidified and dried, mixed and vacuum dried to obtain a mixture; wherein the dehumidification and drying temperature is 170℃ and the time is 8h; the vacuum drying temperature is 170℃.

[0110] After vacuum drying, the moisture content of both the PET chips and the masterbatch was 35 ppm; the content of hydroxyl-terminated polydimethylsiloxane in the mixture was 1.2 wt%.

[0111] (3) Melt spinning the mixture;

[0112] The process flow is as follows: feeding from the hopper → melt extrusion by a twin-screw extruder → conveying the melt by a metering pump → extruding filaments by the spinning assembly → side-blowing cooling → oiling and bundling by the bundling device → guiding by the guide disc → winding by the winding device → drawing by the drawing machine; wherein, the surface energy of the spinneret and its internal metal flow channel inner wall is 45mN / m, the roughness Ra is 0.2μm, and the surface is kept clean and free of oil or oxide layer;

[0113] The relevant process parameters are as follows: screw speed of twin-screw extruder 25 r / min, melt section temperature of twin-screw extruder 300℃, conveying section temperature of twin-screw extruder 310℃, spinning temperature 305℃, spinneret orifice number 36, spinneret orifice diameter 0.5 mm, winding speed 800 m / min, hot plate temperature of drawing mill 80℃, hot plate temperature of drawing mill 160℃, and draw ratio 3.8 times.

[0114] Tests show that, compared to the comparative production line, the pressure of the spinning component is reduced by 17% during the melt spinning process, the intrinsic viscosity of the intermediate product oil-free filament decreases by 0.03 dL / g, and the breaking strength of the final product PET fiber decreases by 9.84%. The only difference between the comparative production line and this embodiment is that no masterbatch is added.

[0115] The intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.85 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 5.5 cN / dtex, and the elongation at break is 10.3%.

[0116] Comparative Example A1

[0117] A method for reducing PET melt spinning pressure, compared with Example A1, differs only in that: the amount of masterbatch added in step (2) is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.3wt%.

[0118] Tests showed that, compared to the control production line, the pressure of the spinning components decreased by 2.3% during melt spinning, the intrinsic viscosity of the intermediate product oil-free filament decreased by 0.005 dL / g, and the breaking strength of the final product PET fiber decreased by 1.6%.

[0119] The final product of melt spinning, PET fiber, has a breaking strength of 6.0 cN / dtex and a breaking elongation of 9.4%.

[0120] Comparative Example A2

[0121] A method for reducing PET melt spinning pressure, compared with Example A3, differs in that: in step (2), the amount of masterbatch added is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 1.5wt%.

[0122] Tests showed that, compared to the control production line, the pressure of the spinning components was reduced by 24.5% during melt spinning, the intrinsic viscosity of the intermediate product oil-free filament decreased by 0.06 dL / g, and the breaking strength of the final product PET fiber decreased by 19.7%.

[0123] The final product of melt spinning, PET fiber, has a breaking strength of 4.9 cN / dtex and a breaking elongation of 8.7%.

[0124] The pressure changes during the spinning process of Examples A1-A3, the comparative production line of Example A1, and Comparative Example A2 are as follows: Figure 1 As shown.

[0125] Comparative Example A3

[0126] A method for reducing PET melt spinning pressure differs from Example A1 in that the masterbatch is replaced. The masterbatch is prepared by granulation after blending PET with methyl-terminated polydimethylsiloxane. The intrinsic viscosity of PET is 1.13 dL / g. The manufacturer of methyl-terminated polydimethylsiloxane is Huangshan Qiangli Chemical Co., Ltd., and the number average molecular weight is 10000 g / mol.

[0127] Tests showed that, compared to the control production line, the spinning component pressure was reduced by 4.8%, the intrinsic viscosity of the intermediate product oil-free filament decreased by 0.03 dL / g, and the breaking strength of the final product PET fiber decreased by 8.2%.

[0128] The final product of melt spinning, PET fiber, has a breaking strength of 5.5 cN / dtex and a breaking elongation of 8.9%.

[0129] Comparative Example A4

[0130] A method for reducing PET melt spinning pressure differs from Example A1 in that: in step (2), the masterbatch is directly replaced with hydroxyl-terminated polydimethylsiloxane (same as Example A1), and the feeding ratio is controlled so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.6wt%.

[0131] Tests showed that, compared to the control production line, the spinning component pressure was reduced by 4.2%, the intrinsic viscosity of the intermediate product oil-free filament decreased by 0.04 dL / g, and the breaking strength of the final product PET fiber decreased by 24.6%.

[0132] The final product of melt spinning, PET fiber, has a breaking strength of 4.6 cN / dtex and a breaking elongation of 8.8%.

[0133] The results from comparative examples A1 to A4 show that when the silicone content is too low (0.3 wt%), it is difficult to form a molecular-level lubricating layer in the high-shear region, resulting in insufficient lubrication, limited pressure reduction effect, and uneven fiber stress. When the silicone content is too high (1.5 wt%), it will cause interfacial lubrication oversaturation, local enrichment to form a slip layer, and stretching instability. Although the pressure reduction increases, the viscosity decreases and mechanical properties are significantly lost. When methyl-terminated polydimethylsiloxane is used, the inertness of the end groups reduces its orderly adsorption on the metal wall, resulting in poor continuity of the lubricating layer, leading to unstable pressure reduction and deterioration of fiber properties. Directly adding hydroxyl-terminated polydimethylsiloxane instead of masterbatch will lead to uneven silicone dispersion, phase separation and bubbles in the melt, discontinuous lubricating layer, and ultimately small pressure reduction and significant decrease in fiber properties.

[0134] This invention also conducted extensive exploratory experiments, replacing hydroxyl-terminated polydimethylsiloxanes from multiple manufacturers. It was found that the number-average molecular weight needed to be strictly controlled within the range of 5000-30000 g / mol. When using the production conditions of Example A1, only adjusting the number-average molecular weight of the hydroxyl-terminated polydimethylsiloxane to 3000 g / mol resulted in a 3.9% reduction in the pressure of the spinning assembly compared to the control production line. The pressure reduction effect was unstable because the low molecular weight led to high volatility, making it difficult to maintain a stable molecular-level lubricating layer during spinning and thus unable to continuously exert its lubricating and pressure-reducing effect. When the number-average molecular weight of the hydroxyl-terminated polydimethylsiloxane was adjusted to 40000 g / mol, the pressure of the spinning assembly only decreased by 5.2% compared to the control production line. The pressure reduction was significantly reduced because the high molecular weight impaired the migration of the hydroxyl-terminated polydimethylsiloxane, making it difficult to distribute evenly to the spinning assembly wall during melt flow, thus failing to form an effective lubricating layer and affecting the pressure reduction effect. This invention also investigated the effect of the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch, and found that its content needs to be strictly controlled within the range of 30±5wt%. When using the production conditions of Example A1, only adjusting the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch to 20wt% resulted in a 4.5% reduction in the pressure of the spinning assembly compared to the control production line. The pressure reduction was too low because the release of hydroxyl-terminated polydimethylsiloxane in the masterbatch was insufficient, resulting in a slow formation rate of the lubricating layer and insufficient interface supply, which could not effectively reduce the frictional resistance between the melt and the metal wall. When the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch was adjusted to 40wt%, although the pressure of the spinning assembly was reduced by 22.8% compared to the control production line, the intrinsic viscosity of the melt decreased and the mechanical properties of the fiber were significantly reduced. This was because the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch was too high, resulting in uneven release of it in the melt, with local areas becoming oversaturated, forming an unstable slip layer, which in turn caused stretching instability and affected the fiber properties.

[0135] Example B1

[0136] A method for improving fiber mechanical properties while reducing PET melt spinning temperature is basically the same as in Example A1, except that: PET chips and carrier PET are replaced, and the intrinsic viscosity of both PET chips and carrier PET is 1.12 dL / g; in step (3), the screw speed of the twin-screw extruder is 30 r / min, and the spinning temperature is 295℃ (10℃ lower than the spinning temperature of pure PET).

[0137] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.94 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 6.26 cN / dtex, and the elongation at break is 8.6%.

[0138] Example B2

[0139] A method for improving fiber mechanical properties while reducing PET melt spinning temperature is basically the same as in Example A2, except that: PET chips and carrier PET are replaced, and the intrinsic viscosity of both PET chips and carrier PET is 1.12 dL / g; in step (3), the screw speed of the twin-screw extruder is 30 r / min, and the spinning temperature is 290℃ (15℃ lower than the spinning temperature of pure PET).

[0140] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.95 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 6.03 cN / dtex, and the elongation at break is 9.4%.

[0141] Example B3

[0142] A method for improving fiber mechanical properties while reducing PET melt spinning temperature is basically the same as in Example A3, except that: PET chips and carrier PET are replaced, and the intrinsic viscosity of both PET chips and carrier PET is 1.12 dL / g; in step (3), the screw speed of the twin-screw extruder is 30 r / min, and the spinning temperature is 290℃ (15℃ lower than the spinning temperature of pure PET).

[0143] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.88 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 6.13 cN / dtex, and the elongation at break is 9.1%.

[0144] Comparing Examples A1 with Examples B1, A2 with Examples B2, and A3 with Examples B3, it can be seen that by adjusting the intrinsic viscosity to 1.12 dL / g, increasing the screw speed to 30 r / min, and lowering the spinning temperature to 290-295℃, the degradation of PET melt is reduced. The fiber breaking strength of Examples B1-B3 is significantly improved compared with Examples A1-A3, achieving a synergistic effect between low-temperature spinning and improved mechanical properties.

[0145] Comparative Example B1

[0146] A method for improving the mechanical properties of fibers, compared with Example B1, differs only in that the amount of masterbatch added in step (2) is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.3wt%.

[0147] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.91 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 5.91 cN / dtex, and the elongation at break is 8.9%.

[0148] Comparative Example B2

[0149] A method for improving the mechanical properties of fibers, compared with Example B3, differs in that: in step (2), the amount of masterbatch added is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 1.5 wt%.

[0150] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.92 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 5.62 cN / dtex, and the elongation at break is 9.8%.

[0151] Comparative Example B3

[0152] A method for improving the mechanical properties of fibers differs from Example B1 in that the masterbatch is replaced. The masterbatch is prepared by granulation after blending PET with methyl-terminated polydimethylsiloxane. The intrinsic viscosity of PET is 1.12 dL / g. The manufacturer of methyl-terminated polydimethylsiloxane is Huangshan Qiangli Chemical Co., Ltd., and the number average molecular weight is 10000 g / mol.

[0153] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.93 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 5.2 cN / dtex, and the elongation at break is 9.5%.

[0154] Comparative Example B4

[0155] A method for improving the mechanical properties of fibers differs from Example B1 in that: in step (2), the masterbatch is directly replaced with hydroxyl-terminated polydimethylsiloxane (same as Example B1), and the feeding ratio is controlled so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.6wt%.

[0156] Tests show that the intrinsic viscosity of the melt-spun intermediate product, oil-free filament, is 0.94 dL / g; the tensile strength of the final melt-spun product, PET fiber, is 5.8 cN / dtex, and the elongation at break is 9.4%.

[0157] The results of comparative examples B1 to B4 show that when the silicone content is too low (0.3 wt%), the lubricating film cannot be formed continuously, and the effect of improving mechanical properties is not obvious. When the silicone content is too high (1.5 wt%), the fiber surface slips and orientation is hindered, resulting in a significant decrease in strength. When methyl-terminated polydimethylsiloxane is used, the compatibility is poor, the lubricating layer is unstable, and the improvement in fiber performance is small. Directly adding hydroxyl-terminated polydimethylsiloxane instead of masterbatch will cause uneven dispersion and local enrichment, resulting in melt pressure fluctuations and weakening fiber strength and stability.

[0158] This invention also conducted extensive exploratory experiments, replacing hydroxyl-terminated polydimethylsiloxanes from multiple manufacturers. It was found that the number-average molecular weight must be strictly controlled within the range of 5000-30000 g / mol; otherwise, the fiber mechanical properties significantly decrease. This invention also investigated the effect of the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch, finding that its content must be strictly controlled within the range of 30±5 wt%; otherwise, the fiber mechanical properties decrease.

[0159] Example C1

[0160] A method for improving the flexibility of polyester fibers is basically the same as in Example A1, except that: the PET chips and carrier PET are replaced, and the intrinsic viscosity of both the PET chips and carrier PET is 1.12 dL / g; the amount of masterbatch added in step (2) is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.3 wt%;

[0161] In step (3), such as Figure 3 As shown, the PET melt spinning process is as follows: feeding from hopper 1 → melt extrusion from twin-screw extruder 2 → conveying melt from metering pump 3 → extruding filaments from spinning assembly 4 → side-blowing cooling → oiling and bundling from bundling device 5 → guiding from guide disc 6 → drafting from three-stage drafting hot rollers 8 (composed of GR1, GR2, and GR3 arranged at intervals along the filament bundle running direction) → winding from winding device 7; the relevant process parameters are: screw speed of twin-screw extruder 30 r / min, melt section temperature of twin-screw extruder 300℃, conveying section temperature of twin-screw extruder 310℃, spinning temperature 305℃, number of spinneret holes 36, spinneret hole diameter 0.5 mm, running speed of GR1 450 m / min, temperature of GR1 80℃, running speed of GR2 1750 m / min, temperature of GR2 160℃, running speed of GR3 1950 m / min, temperature of GR3 165℃.

[0162] Tests show that the elongation at break of the final product PET fiber produced by melt spinning is 23% (compared to 20% for the final product PET fiber produced by melt spinning on the comparative production line; the only difference between the comparative production line and this embodiment is that no masterbatch is added), and the initial modulus is 58 cN / dtex (compared to 66 cN / dtex for the final product PET fiber produced by melt spinning on the comparative production line).

[0163] Example C2

[0164] A method for improving the flexibility of polyester fibers is basically the same as in Example A1, except that: the PET chips and carrier PET are replaced, and the intrinsic viscosity of both the PET chips and carrier PET is 1.12 dL / g; the amount of masterbatch added in step (2) is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.6 wt%;

[0165] In step (3), the PET melt spinning process is as follows: feeding into the hopper → melting and extruding with a twin-screw extruder → conveying the melt with a metering pump → extruding filaments with a spinning assembly → side-blowing cooling → oiling and bundling with a bundling device → guiding with a guide disc → three-stage drawing with hot rollers → winding with a winding device; the relevant process parameters are: the screw speed of the twin-screw extruder is 30 r / min, the melting section temperature of the twin-screw extruder is 300℃, the conveying section temperature of the twin-screw extruder is 310℃, the spinning temperature is 305℃, the number of spinneret holes is 36, the spinneret hole diameter is 0.5 mm, the running speed of GR1 is 450 m / min, the temperature of GR1 is 80℃, the running speed of GR2 is 1650 m / min, the temperature of GR2 is 160℃, the running speed of GR3 is 1900 m / min, and the temperature of GR3 is 165℃.

[0166] Tests show that the elongation at break of the final product PET fiber produced by melt spinning is 30% (compared to 21% for the final product PET fiber produced by melt spinning on the comparative production line; the only difference between the comparative production line and this embodiment is that no masterbatch is added), and the initial modulus is 52 cN / dtex (compared to 68 cN / dtex for the final product PET fiber produced by melt spinning on the comparative production line).

[0167] Example C3

[0168] A method for improving the flexibility of polyester fibers is basically the same as in Example A1, except that: the PET chips and carrier PET are replaced, and the intrinsic viscosity of both the PET chips and carrier PET is 1.12 dL / g; the amount of masterbatch added in step (2) is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.9 wt%;

[0169] In step (3), the PET melt spinning process is as follows: feeding into the hopper → melting and extruding with a twin-screw extruder → conveying the melt with a metering pump → extruding filaments with a spinning assembly → side-blowing cooling → oiling and bundling with a bundling device → guiding with a guide disc → three-stage drawing with hot rollers → winding with a winding device; the relevant process parameters are as follows: the screw speed of the twin-screw extruder is 30 r / min, the melting section temperature of the twin-screw extruder is 300℃, the conveying section temperature of the twin-screw extruder is 310℃, the spinning temperature is 305℃, the number of spinneret holes is 36, the spinneret hole diameter is 0.5 mm, the running speed of GR1 is 450 m / min, the temperature of GR1 is 80℃, the running speed of GR2 is 1700 m / min, the temperature of GR2 is 160℃, the running speed of GR3 is 1850 m / min, and the temperature of GR3 is 165℃.

[0170] Tests show that the elongation at break of the final product PET fiber produced by melt spinning is 28% (compared to 23% for the final product PET fiber produced by melt spinning on the comparative production line; the only difference between the comparative production line and this embodiment is that no masterbatch is added), and the initial modulus is 48 cN / dtex (compared to 70 cN / dtex for the final product PET fiber produced by melt spinning on the comparative production line).

[0171] Comparing Examples C1-C3 with Example A1, it can be seen that by optimizing the silicone content, adjusting the intrinsic viscosity, increasing the screw speed, and adopting a continuous spinning-drawing process, the fiber breaking elongation is significantly improved, the initial modulus is significantly reduced, and the flexibility is significantly better than that of Example A1, which focuses on reducing pressure.

[0172] Comparative Example C1

[0173] A method for improving the flexibility of polyester fibers, which differs from Example C1 only in that the amount of masterbatch added in step (2) is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.1 wt%.

[0174] Tests show that the final product of melt spinning, PET fiber, has a breaking elongation of 22% and an initial modulus of 60 cN / dtex.

[0175] Comparative Example C2

[0176] A method for improving the flexibility of polyester fibers, compared with Example C3, differs in that: in step (2), the amount of masterbatch added is adjusted so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 1.2 wt%.

[0177] Tests show that the final product of melt spinning, PET fiber, has a breaking elongation of 21% and an initial modulus of 59 cN / dtex.

[0178] Comparative Example C3

[0179] A method for improving the flexibility of polyester fibers differs from Example C1 in that the masterbatch is replaced. The masterbatch is prepared by granulation after blending PET with methyl-terminated polydimethylsiloxane. The intrinsic viscosity of PET is 1.13 dL / g. The manufacturer of methyl-terminated polydimethylsiloxane is Huangshan Qiangli Chemical Co., Ltd., and the number average molecular weight is 10000 g / mol.

[0180] Tests show that the final product of melt spinning, PET fiber, has a breaking elongation of 22% and an initial modulus of 62 cN / dtex.

[0181] Comparative Example C4

[0182] A method to improve the flexibility of polyester fiber, which differs from Example C1, is as follows: in step (2), the masterbatch is directly replaced with hydroxyl-terminated polydimethylsiloxane (same as Example C1), and the feeding ratio is controlled so that the content of hydroxyl-terminated polydimethylsiloxane in the mixture is 0.6wt%.

[0183] Tests show that the final product of melt spinning, PET fiber, has a breaking elongation of 19% and an initial modulus of 61 cN / dtex.

[0184] The results of comparative examples C1 to C4 show that when the silicone content is too low (0.1 wt%), the improvement in flexibility is limited; when the silicone content is too high (1.2 wt%), the fiber surface becomes slippery and the orientation is insufficient, thus limiting the improvement in flexibility; when methyl-terminated polydimethylsiloxane is used, the compatibility is poor and the improvement in flexibility is significantly lower than that of hydroxyl-terminated silicone; directly adding hydroxyl-terminated polydimethylsiloxane instead of masterbatch will cause uneven silicone dispersion, thus limiting the improvement in flexibility.

[0185] This invention also conducted extensive exploratory experiments to investigate the effect of the content of hydroxyl-terminated polydimethylsiloxane in the masterbatch. It was found that its content needs to be strictly controlled within the range of 30±5wt%, otherwise the flexibility will decrease significantly and become unstable.

Claims

1. A method for improving the flexibility of polyester fibers, characterized in that, During the PET melt spinning process, 0.3wt%-0.9wt% of silicone is introduced into the PET melt; The silicone is hydroxyl-terminated polydimethylsiloxane. The silicone is added in the form of a masterbatch, which consists of a carrier PET and silicone. The silicone content in the masterbatch is 30wt%±5wt%. The intrinsic viscosity of PET is 1.12 dL / g, and the intrinsic viscosity of the carrier in the masterbatch is the same as that of PET. The process flow of PET melt spinning includes: twin-screw extruder melt extrusion → side-blown cooling → oiling → three-stage drawing hot roller drawing → winding. The screw speed of the twin-screw extruder for PET melt spinning is 30 r / min.

2. The method for improving the flexibility of polyester fibers according to claim 1, characterized in that, The number average molecular weight of silicone is 5000-30000 g / mol.

3. The method for improving the flexibility of polyester fibers according to claim 1, characterized in that, Introducing silicone into PET melt is achieved by mixing PET chips with masterbatch, followed by drying and melt blending.

4. The method for improving the flexibility of polyester fibers according to claim 3, characterized in that, Vacuum drying is used, and the drying temperature is 160-175℃. After drying, the moisture content of both PET chips and masterbatch is less than 50ppm.

5. The method for improving the flexibility of polyester fibers according to claim 3, characterized in that, Both PET chips and masterbatch are dehumidified and dried before mixing. The dehumidification and drying process is carried out at a temperature of 160-175℃ for 6-10 hours.

6. The method for improving the flexibility of polyester fibers according to claim 1, characterized in that, The surface energy of the spinneret and its internal metal flow channel wall is 35-55 mN / m, the roughness Ra is 0.05-0.25 μm, and the surface is kept clean and free of oil or oxide layer.

7. The method for improving the flexibility of polyester fibers according to claim 1, characterized in that, The spinning temperature for PET melt spinning is 305℃.

8. A method for improving the flexibility of polyester fibers according to any one of claims 1 to 7, characterized in that, The initial modulus of PET fiber, the final product of PET melt spinning, is 48~58 cN / dtex, and the elongation at break is 23%~30%.

Images