High-speed spinning polybutylene terephthalate resin and preparation method thereof

Abstract

The invention discloses polybutylene terephthalate resin capable of being spun at a high speed, and the resin is formed by carrying out polycondensation on regenerated terephthalic acid (r-PTA) and 1, 4-butanediol (BDO), the terephthalic acid is regenerated terephthalic acid (r-PTA), and the content of p-toluic acid (p-TA) is less than or equal to 30 ppm; the content of 4-carboxybenzaldehyde (4-CBA) is less than or equal to 10ppm; the intrinsic viscosity (IV) of the resin is from 0.80 to 1.15 dL / g; the terminal carboxyl group content (AV) is less than or equal to 20mol / t; and a molecular weight distribution index (PDI = Mw / Mn) of 1.8 to 2.2. The PBT resin has the characteristics of narrow molecular weight distribution, high melting point and low acid value, and supports 2000-2200m / min high-speed spinning, and the prepared DTY (draw textured yarn) fiber is high in crimp shrinkage rate (good in elasticity) and good in hydrolysis-resistant stability, is widely applied to the field of textile fibers, and is particularly suitable for production of high-end high-elastic fabrics.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis and processing technology, and in particular to a high-speed spun polybutylene terephthalate resin and its preparation method. Background Technology

[0002] Polybutylene terephthalate (PBT) is one of the five major engineering plastics. Among them, medium-to-high viscosity PBT with an intrinsic viscosity (IV) of 0.80~1.15 dL / g is the most widely used, covering fields such as injection molding modification, films, and textile fibers.

[0003] With the advancement of the "dual carbon" goal, the preparation of PBT using recycled terephthalic acid (r-PTA) has become a hot topic in the industry. However, recycled polybutylene terephthalate resin (r-PBT) prepared by existing technologies generally suffers from a wide molecular weight distribution (PDI>2.5) and a low melting point. This is because recycled raw materials often contain residual isomers (such as isophthalic acid) or others, which disrupt the regularity of the molecular chain, resulting in a melting point typically below 220℃. This leads to insufficient heat resistance of the fibers during post-processing (such as texturing and setting). The wide molecular weight distribution of the resin results in uneven melt strength, making it prone to filament slippage or breakage during melt spinning if the spinning speed exceeds 1800m / min. Simultaneously, the uneven internal crystal orientation of the resin fibers makes it difficult to improve the crimp shrinkage rate (CC%) of the resulting elastic yarns (stretch textured yarns, DTY), failing to meet the demands of high-end, high-elasticity fabrics.

[0004] Therefore, developing a recycled PBT resin with good elasticity, high melting point, and the ability to overcome the 2000m / min spinning speed bottleneck is of great significance for improving the production efficiency and product quality of the recycled fiber industry. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing production processes, the applicant provides a high-speed spinning polybutylene terephthalate resin and its preparation method. Using regenerated terephthalic acid (r-PTA) with p-TA ≤ 30 ppm and 4-CBA ≤ 10 ppm as raw material, and without solid-phase thickening (SSP) treatment, a PBT resin with narrow molecular weight distribution, high melting point, and low acid value is prepared. This resin can meet the processing requirements of high-speed spinning and high-elasticity fibers.

[0006] The technical solution adopted in this invention and its beneficial effects are as follows: This application provides a high-speed spun polybutylene terephthalate resin, wherein the resin is formed by the condensation polymerization of recycled terephthalic acid (r-PTA) and 1,4-butanediol (BDO); ​​wherein the terephthalic acid is recycled terephthalic acid (r-PTA), and the content of p-methylbenzoic acid (p-TA) is ≤30ppm; the content of p-carboxybenzaldehyde (4-CBA) is ≤10ppm; the intrinsic viscosity (IV) of the resin is 0.80 to 1.15 dL / g; the terminal carboxyl group content (AV) is ≤20mol / t; and the molecular weight distribution index (PDI=Mw / Mn) is 1.8 to 2.2. By limiting p-TA to ≤30ppm, 4-CBA to ≤10ppm, IV to 0.80-1.15dL / g, PDI to 1.8-2.2, and AV to ≤20mol / t, a synergistic effect is achieved. p-TA ≤30ppm prevents premature end-capping of molecular chains, while 4-CBA ≤10ppm ensures uniform catalyst activity. Together, they ensure synchronous molecular chain growth, preventing PDI widening from the source. IV = 0.80-1.15dL / g balances melt flowability and strength, allowing the melt to pass smoothly through the spinneret while resisting high-speed stretching tension, avoiding breakage due to excessive thinning and pore blockage due to excessive thickening. The narrow distribution of PDI = 1.8-2.2 ensures uniform molecular chain length, stable melt rheology, and uniform filament stress during high-speed spinning, preventing filament drift and breakage. Simultaneously, the fiber crystallization orientation is synchronized, easily forming a regular crimped structure. AV ≤20mol / t inhibits hydrolysis, avoids high-temperature melt degradation and fiber crimping and relaxation, and ensures long-term stability. Ultimately, stable spinning at 2000-2200m / min was achieved, with DTY crimp shrinkage exceeding 40%, solving the pain points of traditional recycled PBT such as "difficulty in high-speed spinning and insufficient elasticity".

[0007] The intrinsic viscosity (IV) of the resin is 0.90 to 1.15 dL / g; the terminal carboxyl group content (AV) is ≤15 mol / t. Further optimization of molecular weight and hydrolytic stability, with an optimal IV value range better suited to the melt strength requirements of high-speed spinning, and AV ≤15 mol / t significantly improving the fiber's resistance to damp heat aging, ensuring a long-term stable crimp shrinkage rate >45%, meeting the long-term use requirements of high-end fabrics.

[0008] The resin has a melting peak temperature (Tm) of 222 to 226°C. High-melting-point resins are less prone to melting and deformation during heat setting, forming a stable spiral coil structure and improving the durability of the coil shrinkage rate. Simultaneously, it prevents fiber adhesion during high-temperature setting, ensuring efficient cooling and curing during high-speed spinning.

[0009] The initial hue b* value of the resin is ≤6.0. Resins with excellent hue have complete molecular chain structures and no excessive degradation products (short chains), ensuring melt uniformity and fiber dyeing uniformity; avoiding localized color differences in the curled structure caused by poor hue, and improving the appearance quality of high-end fabrics.

[0010] After the resin is kept at a constant temperature of 250°C for 30 minutes, the change rate of its melt flow rate (MVR) is ≤10.0%. Resins with a low MVR change rate have good thermal stability, no significant degradation during high-speed spinning (when the melt is kept at a high temperature for a long time), stable melt viscosity, and avoid breakage or filament drift caused by stress fluctuations during drawing, thus ensuring the continuity of high-speed spinning.

[0011] The r-PTA has specific stable carbon isotope characteristics, its δ 13 The carbon value ranges from -24‰ to -27‰. Raw material traceability is achieved through carbon isotope characteristics, ensuring the use of qualified r-PTA and guaranteeing product performance consistency; it also distinguishes it from petrochemical v-PTA (δ¹⁴ PTA). 13 C = -28‰ to -30‰).

[0012] The resin can be used to prepare textile fibers, such as POY, FDY, or drawn textured yarn (DTY). It is clearly understood that the resin is suitable for processing various textile fibers, especially for the drawn textured yarn process of DTY. Its narrow PDI and high melting point characteristics allow it to form a regular crimped structure through false twisting, providing process adaptability for subsequent high crimp shrinkage rates.

[0013] The fiber is DTY, with a total fineness of 20 to 200 denier and a crimp shrinkage rate (CC%) >40%. The wide range of fineness coverage meets the needs of various scenarios, and the crimp shrinkage rate >40% directly meets the elasticity requirements of high-end high-elastic fabrics, solving the industry pain points of "stiff fibers" and "insufficient elasticity" of existing recycled PBT fibers.

[0014] When the fiber is DTY, the spinning speed is ≥2000m / min. Compared with traditional recycled materials (1500-1800m / min), the production capacity is increased by more than 20%, meeting the high-efficiency production needs of the textile industry and enhancing the market competitiveness of products.

[0015] The present invention also provides a method for preparing the high-speed spun polybutylene terephthalate resin, comprising the following steps: (1) Esterification: r-PTA and BDO are mixed in a molar ratio of 1:1.3~1.8 and esterified at atmospheric pressure at 225-235℃ under the action of a titanium catalyst. (2) Polycondensation: The esterified material is heated to 250-260℃ and polycondensation reaction is carried out under vacuum conditions with an absolute pressure of <50Pa for 130-180 minutes.

[0016] The PBT resin of this invention avoids the problems of high energy consumption and poor color change caused by the SSP process. It has the characteristics of narrow molecular weight distribution, high melting point and low acid value, and supports high-speed spinning of 2000-2200m / min. The DTY (stretch textured yarn) fibers prepared have high crimp shrinkage (good elasticity) and good hydrolytic stability. It is widely used in the textile fiber field, especially suitable for the production of high-end high-elastic fabrics.

[0017] The use of polybutylene terephthalate (PBT) resin of this invention to prepare textile fibers significantly increases spinning speed. The narrow PDI characteristic of this invention results in highly uniform melt rheological behavior, enabling high-speed spinning of 2000-2200 m / min, increasing production capacity by more than 20% compared to traditional recycled materials (approximately 1500-1800 m / min). The extremely high melting point and regular structure ensure uniform internal crystal orientation of the fiber, resulting in DTY with high crimp shrinkage (>40%), good elasticity, and uniform dyeing, solving the "stiff fiber" problem. The extremely low end carboxyl group content (≤20 mol / t) significantly slows down the resin degradation rate under humid and hot environments, resulting in a long hydrolytic lifespan for the prepared product. Simultaneously, this invention eliminates the energy-intensive SSP process, shortening the production flow and making the process more environmentally friendly and efficient. Detailed Implementation

[0018] The high-speed spun polybutylene terephthalate (PBT) resin of this invention is formed by the condensation polymerization of recycled terephthalic acid (r-PTA) and 1,4-butanediol (BDO). The p-methylbenzoic acid (p-TA) content is ≤30 ppm, and the p-carboxybenzaldehyde (4-CBA) content is ≤10 ppm. The low p-TA content eliminates the end-blocking effect of chain growth, allowing all molecular chains to grow synchronously at similar rates.

[0019] The intrinsic viscosity (IV) of the PBT resin of this invention is controlled between 0.80 and 1.15 dL / g, preferably between 0.90 and 1.15 dL / g. This range ensures both melt flowability and sufficient melt strength to support high-speed drawing. The molecular weight distribution index (PDI = Mw / Mn) is controlled between 1.8 and 2.2. A narrow distribution means that the resin contains very few oligomers that easily lead to crystallization and network blockage, and also contains no ultra-high molecular weight components that easily lead to drawing breakage. The terminal carboxyl group content (AV) is ≤20 mol / t, preferably ≤15 mol / t. This is achieved through a highly active catalytic system under a short thermal history, significantly improving the resin's hydrolytic stability. The resin's melting peak temperature (Tm) is 222 to 226 °C. This indicates that isomers in the recycled raw materials are effectively removed, and the molecular chain regularity is extremely high. The resin also exhibits excellent appearance and processing stability: initial hue b* value ≤ 6.0; melt flow rate (MVR) change rate ≤ 10.0% after holding at 250℃ for 30 minutes.

[0020] The method for preparing the high-speed spun polybutylene terephthalate (PBT) resin of the present invention employs a low-temperature, high-vacuum, and rapid reaction direct melting process, and the specific steps include: (1) Esterification stage: r-PTA and BDO are mixed in a molar ratio of 1:1.3~1.8 and esterified at atmospheric pressure at 225-235℃ under the action of titanium catalyst.

[0021] (2) Polycondensation stage: The esterified material is heated to 250-260℃ and polycondensation reaction is carried out under high vacuum conditions with an absolute pressure of <50Pa. The reaction time can be controlled within 130-180 minutes to reach the target viscosity, without the need for subsequent solid-phase thickening.

[0022] Textile fibers prepared using the high-speed spun polybutylene terephthalate (PBT) resin of the present invention, wherein the fibers are POY, FDY, or drawn textured yarn (DTY). Benefiting from the narrow distribution characteristics of the resin, when preparing DTY, the total fineness of the fibers can cover a wide range from 20 to 200 deniers, and the crimp shrinkage (CC%) is >40%, exhibiting excellent high elastic recovery properties.

[0023] The r-PTA described in this invention is recycled terephthalic acid obtained from waste polyester clothing as a base material through an enzymatic depolymerization and crystallization purification process or a photocatalytic degradation and multi-stage refining process. The r-PTA prepared by enzymatic depolymerization was purchased from Nanjing Suxin Technology Co., Ltd.; the r-PTA prepared by photocatalytic degradation was purchased from DePoly SA, Switzerland. v-PTA is terephthalic acid synthesized from fossil resources such as petroleum and natural gas through a p-xylene (PX) liquid-phase oxidation process.

[0024] The specifications of the main raw materials used in the embodiments and comparative examples of the present invention are shown in Table 1. 1,4-Butanediol (BDO) was selected as a superior grade with a purity ≥99.7%, and the catalyst was selected as tetrabutyl titanate (TBT) with a purity ≥99.0%.

[0025] Table 1: code name type p-TA content (ppm) 4-CBA content (ppm) <![CDATA[δ 13 C value]]> r-PTA-1 This invention / enzymatic hydrolysis method 12 2.5 -26.2‰ r-PTA-2 This invention / photolysis method 25 8.0 -26.4‰ v-PTA Comparative / Petrochemical Grade 150 25 -28.5‰ The specific testing methods are as follows (all quantitative analyses were performed in at least three parallel experiments, and the average value was taken): 1. Intrinsic Viscosity (IV) Test Method: Refer to ISO 1628-5 or GB / T 14190-2017. The equipment used is an automatic Ubbelohde viscometer. A phenol / 1,1,2,2-tetrachloroethane (1:1) solvent is used, dissolved at 110-120℃ for 30 minutes. The outflow time is measured in a constant temperature water bath at 25.00℃, and calculated using the Solomon-Ciuta formula. 2. Terminal carboxyl group content (AV) test method: Refer to FZ / T50012-2006 for details. Weigh 1.0 g of sample and dissolve it in 50 mL of o-cresol / chloroform (7:3) mixed solvent (reflux at 90℃). After cooling, add 0.1% bromocresol green indicator. Titrate with a standardized 0.05 mol / L potassium hydroxide-ethanol standard solution until the solution changes from pale yellow to blue-green and does not fade within 30 seconds.

[0026] 3. Molecular weight distribution (PDI) determination: Gel permeation chromatography (GPC) was used, with hexafluoroisopropanol (HFIP) as the solvent. PMMA standard was selected as the test standard. The calculation formula is PDI = weight-average molecular weight (Mw) / number-average molecular weight (Mn).

[0027] 4. Determination of melting peak temperature (Tm): Differential scanning calorimetry (DSC) was used. The method was in accordance with GB / T19466.3-2004. Under a nitrogen atmosphere, the temperature was increased to 260℃ at 10℃ / min, the thermal history was eliminated, and then the temperature was lowered. The temperature was then increased again at 10℃ / min, and the melting peak temperature of the second heating curve was recorded.

[0028] 5. Content Determination (4-CBA and p-TA): An Agilent 1260 high-performance liquid chromatograph (HPLC) was used. The chromatographic column was an Agilent ZORBAX Eclipse Plus C18 (4.6 × 250 mm, 5 μm). The mobile phase was 0.5% ammonium acetate solution in phase A and methanol in phase B. A gradient elution program was used. 0.2 g of sample was weighed, added with ammonia, and digested in a sealed container at 125 °C for 2.5 hours. After cooling and making up to volume, the sample was filtered and injected. The detection wavelength was 254 nm.

[0029] 6. Stable carbon isotopes (δ¹²) 13 C) Measurement: The instrument used was an elemental analyzer (EA) coupled with an isotope ratio mass spectrometer (IRMS). The testing standard was based on Vienna Piddistone (VPDB). The testing accuracy was SD ≤ 0.15‰.

[0030] 7. Hue Test (b) *Test: The instrument selected is the HunterLab spectrophotometer, the test mode is reflection mode, and the light source is the standard D65 light source.

[0031] 8. Curl Shrinkage (CC%) Test: Refer to GB / T6506-2001 for specific methods. Test the length change of DTY fibers before and after boiling water treatment, and calculate their elastic recovery ability.

[0032] 9. Melt Flow Rate (MVR) Test: Pretreatment: The sample to be tested is vacuum dried at 120 degrees Celsius for more than 4 hours to ensure that the moisture content is less than 0.002% (20ppm) to eliminate the influence of moisture on the test results.

[0033] Initial MVR test (benchmark value): The initial melt volumetric flow rate of the sample was measured using a melt flow rate meter at 250 degrees Celsius and a load of 2.16 kg, and recorded as MVR_0.

[0034] Isothermal residence test: Samples from the same batch are loaded into a barrel and forcibly maintained at a constant temperature of 250 degrees Celsius for 30 minutes. During this period, the material is in a high-temperature molten state. If the molecular chains break or degrade, its fluidity will change significantly.

[0035] MVR test after dwell: Immediately after the dwell ends, the melt volume flow rate is measured and recorded as MVR_1.

[0036] Calculation formula: MVR change rate (percentage) = (MVR_1 - MVR_0) / MVR_0 × 100%.

[0037] The embodiments and comparative examples of this invention were all conducted in a 30L stainless steel polymerization reactor equipped with a distillation column and a high vacuum system. The raw materials were 7.55 kg of r-PTA (or v-PTA) and 7.37 kg of BDO (molar ratio 1:1.8).

[0038] Example 1: Using r-PTA-1 from Table 1 as raw material, the intrinsic viscosity was IV 0.92 dl / g, the terminal carboxyl group AV was 10.5 mol / t, the PDI distribution was 2.02, the melting point Tm was 224.1℃, and the MVR change rate was 2.5%.

[0039] The specific steps for preparing PBT include: (1) Esterification stage: r-PTA-1 and BDO are mixed at a molar ratio of 1:1.8, and the catalyst is TBT with an addition amount of 8.0g (800ppm). Under the action of titanium catalyst, the esterification reaction is carried out at atmospheric pressure at 230℃.

[0040] (2) Polycondensation stage: The esterified material is heated to 255°C and polycondensation reaction is carried out under high vacuum conditions with an absolute pressure of <50Pa. The target viscosity is reached after 150 minutes of reaction and the material is discharged.

[0041] Example 2: Using r-PTA-2 from Table 1 as raw material, after polycondensation for 170 minutes, the material was directly discharged. The intrinsic viscosity IV was 1.12 dl / g, the terminal carboxyl group AV was 13.5 mol / t, the PDI distribution was 2.15, the melting point Tm was 223.8℃, and the MVR change rate was 3.8%.

[0042] Example 3: Using r-PTA-1 from Table 1 as raw material, after polycondensation for 180 minutes, the material was directly discharged. The intrinsic viscosity IV was 1.02 dl / g, the terminal carboxyl group AV was 12.8 mol / t, the PDI distribution was 2.08, the melting point Tm was 224.2℃, and the MVR change rate was 3.0%.

[0043] Comparative Example 1: Using v-PTA from Table 1 as raw material, the product was discharged directly after polycondensation for 190 minutes. The intrinsic viscosity (IV) is 1.02 dl / g, the terminal carboxyl group (AV) is 22 mol / t, the PDI distribution is 2.35, the melting point (Tm) is 224.5℃, and the MVR change rate is 6.5%.

[0044] Comparative Example 2: A commercially available ordinary recycled PBT product, specification R-L10XM, from Jiangsu Heshili New Materials Co., Ltd. Direct testing yielded an intrinsic viscosity (IV) of 1.02 dl / g, terminal carboxyl group AV of 28 mol / t, PDI distribution of 2.7, melting point (Tm) of 220.4℃, and MVR change rate of 15.0%.

[0045] Comparative Example 3: Using v-PTA from Table 1 as raw material, the material was discharged directly after polycondensation for 210 minutes. The intrinsic viscosity IV was 1.21 dl / g, the terminal carboxyl group AV was 18 mol / t, the PDI distribution was 2.19, the melting point Tm was 224.1℃, and the MVR change rate was 3.8%.

[0046] The PBT resins of the final embodiment and comparative example were tested using the methods described above, and the physical properties are shown in Table 2.

[0047] Table 2: project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Source of raw materials r-PTA-1 r-PTA-2 r-PTA-1 v-PTA Ordinary regeneration r-PTA-1 Application directions 50D Fine Denier 150D Coarse Denier 75D Standard 50D Fine Denier 50D Fine Denier 50D Fine Denier Intrinsic viscosity IV (dl / g) 0.92 1.12 1.02 1.02 1.02 1.21 Terminal carboxyl group AV (mol / t) 10.5 13.5 12.8 22.0 28.0 18 PDI distribution 2.02 2.15 2.08 2.35 2.70 2.19 Melting point Tm (°C) 224.1 223.8 224.2 224.5 220.4 224.1 * 4.2 4.8 4.5 2.7 8.5 4.9 MVR change rate 2.5% 3.8% 3.0% 6.5% 15.0% 3.8% To verify the spinning performance of stretch textured yarn (DTY), the first step was to prepare PBT pre-oriented yarn (POY). The specific steps are as follows: Slice pretreatment: PBT slices are placed in a drying system for continuous drying, and the final moisture content of the slices is controlled to be ≤20ppm to prevent hydrolysis and degradation during melt extrusion.

[0048] Melt extrusion: The dried chips enter the screw extruder, and the temperature of each zone is controlled at 240℃~265℃. The melt is accurately metered by the metering pump and then enters the spinning assembly.

[0049] Cooling and solidification: The melt is ejected from the spinneret to form a fine stream, which is cooled by side blowing, with the air velocity controlled at 0.3 m / s to 0.5 m / s. By adjusting the air temperature and air pressure, the fibers maintain a low degree of crystallinity and a uniform degree of orientation during the cooling process.

[0050] Oiling and winding: After cooling, the filaments are coated with a special spinning oil by an oiling device, and finally wound by a winding machine at a speed of 1500m / min to 2300m / min to obtain PBT-POY raw yarn.

[0051] Next, PBT drawn textured yarn (DTY) is prepared. The POY precursor yarn is processed using a false-twist texturer, with a draw ratio (DR) set to 1.40–1.70 to ensure sufficient mechanical properties while maintaining elongation at break. Heat setting treatment: The yarn undergoes heat setting in a first heating chamber at 160°C–180°C, utilizing PBT's low glass transition temperature to impart a helical crimp structure. The yarn then undergoes stress relief treatment in a second heating chamber, with the temperature set to 0°C (off) or 140°C–160°C depending on elasticity requirements. The friction disc speed ratio (D / Y ratio) is controlled between 1.6 and 2.0 to ensure uniform twist and shrinkage rate at high speeds. Forming and winding: The false-twist textured fiber is thickened through a network nozzle or directly wound to obtain a highly elastic PBT-DTY finished product.

[0052] Table 3 records the specific DTY specifications, spinning speed, component life, and crimp shrinkage test results of the final PBT-DTY products used in the examples and comparative examples: Table 3: Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 DTY Specifications 50D / 72F 150D / 48F 75D / 36F 50D / 72F 50D / 72F 50D / 72F Spinning speed 2200 2000 2100 1800 1500 1600 Running status Stablize Stablize Stablize Occasionally there are floating threads Frequent decapitation Frequent decapitation Component lifespan (days) 35 30 32 20 5 (Blocking Network) 27 curl shrinkage rate 45.5% 48.2% 46.5% 38.0% 30.5% 41.5% Examples 1, 2, and 3 of this invention cover three viscosity ranges: low, high, and medium. Data shows that using regenerated terephthalic acid (r-PTA) with a p-methylbenzoic acid (p-TA) content ≤30ppm and a p-carboxybenzaldehyde (4-CBA) content ≤10ppm as raw material, combined with a direct melting process, and controlling the terminal carboxyl group content (AV) below 15mol / t (10.5-13.5), the final PBT resin's PDI can be controlled within a narrow range of 2.02-2.15.

[0053] The Tm values ​​of all three embodiments remained stable between 223.8°C and 224.2°C, falling within the high melting point range of 222-226°C. This is comparable to Comparative Example 1 (224.5°C) using petrochemical virgin feedstock, and significantly higher than Comparative Example 2 (220.4°C) using ordinary recycled feedstock. This indicates that the recycled r-PTA feedstock avoids copolymerization degradation and imparts a perfect crystal structure to the resin, which is the basis for the heat-resistant shaping of downstream fibers.

[0054] The terminal carboxyl group content (AV) of all three embodiments was controlled below 15 mol / t (10.5-13.5), far lower than the 22.0 mol / t of Comparative Example 1. This significantly extended the service life of the final fiber product in humid and hot environments.

[0055] The b* values ​​of the resins in the three embodiments were controlled between 4.2 and 4.8, close to the level of virgin materials, and far better than the ordinary recycled material in Comparative Example 2 (b* value of 8.5). This is because the present invention avoids thermal oxidation and yellowing caused by prolonged high-temperature baking in the SSP process.

[0056] When DTY was prepared using the polybutylene terephthalate resin (PBT) of the present invention, the crimp shrinkage rate (CC%) of all three examples was >40%. This shows that the narrow-distribution resin can form a more uniform oriented crystalline network during stretching, giving the fiber stronger resilience and memory, resulting in excellent high-elasticity recovery performance and solving the "stiff filament" problem. Its total fiber fineness can cover a wide range from 20 to 200 deniers, making the product widely applicable. Examples 1-3 all achieved high-speed production at ≥2000 m / min (2000~2200 m / min), and the component life was extended from 20 days to 35 days, with production efficiency increased by more than 20%. In contrast, Comparative Example 1 showed filament drift at 1800 m / min, and Comparative Example 2 could only barely operate at 1500 m / min. Narrow distribution effectively eliminates the risk of melt fracture caused by high molecular weight components, ensures uniform melt rheological behavior, and ensures that all molecular chains bear the same tensile stress, which can stably withstand high-speed tensile stress, extend component life, and improve production efficiency.

[0057] Compared with Comparative Example 1, Comparative Example 1 had p-TA=150ppm and 4-CBA=25ppm in v-PTA, which hindered chain growth and required an extended polycondensation time of 190 minutes (Example 1 only 150 minutes). The prolonged high temperature caused partial thermal degradation of ester bonds, generating short-chain components with a PDI of 2.35 (wider than 2.02 in Example 1). The short-chain components generated by thermal degradation reduced the overall melt strength. When the spinning speed was increased to 1800 m / min, the short-chain regions could not withstand the stretching stress, resulting in filament drift. In contrast, Example 1 did not experience excessive thermal degradation, had uniform melt strength, and could operate stably up to 2200 m / min. Furthermore, Comparative Example 1 had an AV of 22 mol / t (higher than 10.5 mol / t in Example 1), and the high acid value resulted in poor fiber hydrolysis resistance. Under humid and hot conditions, the crimp structure was prone to loosening, and the crimp shrinkage rate was only 38.0%.

[0058] Comparing Example 1 with Comparative Example 3, it can be seen that Comparative Example 3 only controls the content of p-methylbenzoic acid (p-TA) to ≤30ppm and the content of p-carboxybenzaldehyde (4-CBA) to ≤10ppm. Under the condition of high intrinsic viscosity (IV), the polycondensation time needs to be extended to 210 minutes. Excessive polycondensation leads to the cross-linking of some molecular chains to form ultra-high molecular weight components, resulting in uneven melt flow resistance, stress concentration during stretching, and spinning can only barely run at 1600m / min, and there is a problem of frequent breakage. It can be seen that it is necessary to control the p-TA content, 4-CBA content and the intrinsic viscosity (IV) of the resin to 0.80 to 1.15dL / g at the same time to ensure that PDI is controlled within the range. The reason for this is that the synergistic effect of the three factors ensures synchronous growth and uniform termination of molecular chains, preventing the widening of the molecular weight distribution (PDI) from the source, and ultimately adapting to the needs of high-speed spinning. Controlling p-TA ≤ 30ppm can prevent premature and uneven chain growth termination, controlling 4-CBA ≤ 10ppm can prevent uneven chain growth rate, and controlling IV = 0.80-1.15dL / g can prevent uneven degradation caused by excessive chain growth. The essence of a narrow PDI distribution (1.8-2.2) is that the growth process of all molecular chains is completely synchronized, and the control of the three factors forms a closed loop. The control of 4-CBA ensures consistent catalyst activity throughout the polycondensation initiation process, and all molecular chains start the transesterification reaction simultaneously. The control of p-TA prevents premature end-capping of some chains during polycondensation growth, and all molecular chains grow at the same rate. The control of IV value prevents chain breakage caused by thermal degradation. At the termination of polycondensation, the control of IV value ensures that all molecular chains terminate synchronously when they reach the target molecular weight, without excessively long chains or short chains that do not meet the target. Comparative Example 3 had an excessive IV value, with the polycondensation time extended to 210 minutes, triggering thermal degradation. Some long chains broke into shorter chains, resulting in a high PDI and uneven melt strength. Excessive tensile stress in the long-chain regions and insufficient strength in the short-chain regions led to frequent breakage, highlighting the necessity of simultaneous control of the IV value. Furthermore, Comparative Example 3 exhibited a curl shrinkage rate of only 41.5%, likely due to the difficulty in fully stretching and deforming the ultra-high molecular weight component during heat setting, while the low molecular weight component (thermal degradation products) easily slipped, resulting in an irregular curl structure.

[0059] The above description is an explanation of the present invention and not a limitation thereof. The present invention can be modified in any form without departing from its spirit.

Claims

1. A high-speed spun polybutylene terephthalate resin, characterized in that: The resin is formed by the condensation polymerization of terephthalic acid and 1,4-butanediol (BDO); ​​the terephthalic acid is recycled terephthalic acid (r-PTA), and the content of p-methylbenzoic acid (p-TA) is ≤30ppm; the content of p-carboxybenzaldehyde (4-CBA) is ≤10ppm; the intrinsic viscosity (IV) of the polybutylene terephthalate resin is 0.80 to 1.15 dL / g; the terminal carboxyl group content (AV) is ≤20mol / t; and the molecular weight distribution index (PDI=Mw / Mn) is 1.8 to 2.

2.

2. The high-speed spun polybutylene terephthalate resin according to claim 1, characterized in that: The intrinsic viscosity (IV) of the polybutylene terephthalate resin is 0.90 to 1.15 dL / g; the terminal carboxyl group content (AV) is ≤15 mol / t.

3. The high-speed spun polybutylene terephthalate resin according to claim 1, characterized in that: The melting peak temperature (Tm) of the polybutylene terephthalate resin is 222 to 226 °C.

4. The high-speed spun polybutylene terephthalate resin according to claim 1, characterized in that: The initial hue b* value of the polybutylene terephthalate resin is ≤6.

0.

5. The high-speed spun polybutylene terephthalate resin according to claim 1, characterized in that: The polybutylene terephthalate resin, after being held at 250°C for 30 minutes, exhibits a melt flow rate (MVR) change rate ≤10.0%.

6. The high-speed spun polybutylene terephthalate resin according to claim 1, characterized in that: The regenerated terephthalic acid (r-PTA) has specific stable carbon isotope characteristics, its δ 13 The C value ranges from -24‰ to -27‰.

7. The high-speed spun polybutylene terephthalate resin according to claim 1, characterized in that: The polybutylene terephthalate resin can be used to prepare textile fibers, wherein the fibers are POY, FDY or drawn textured yarn (DTY).

8. The high-speed spun polybutylene terephthalate resin according to claim 7, characterized in that: The fiber is DTY, with a total fiber fineness of 20 to 200 denier and a crimp shrinkage rate (CC%) > 40%.

9. The high-speed spun polybutylene terephthalate resin according to claim 7, characterized in that: When the fiber is DTY, the spinning speed is ≥2000m / min.

10. A method for preparing the high-speed spun polybutylene terephthalate resin according to claims 1-9, characterized in that: Includes the following steps: (1) Esterification: r-PTA and BDO are mixed in a molar ratio of 1:1.3~1.8 and esterified at atmospheric pressure at 225-235℃ under the action of a titanium catalyst. (2) Polycondensation: The esterified material is heated to 250-260℃ and polycondensation reaction is carried out under vacuum conditions with an absolute pressure of <50Pa for 130-180 minutes.