A high intrinsic viscosity polybutylene terephthalate resin free of solid-phase tackification, its preparation method and product

Abstract

The application discloses a high-IV PBT resin without solid-phase tackifying, which is prepared by melt polycondensation of terephthalic acid component and 1,4-butanediol component, and is not subjected to solid-phase tackifying (SSP) treatment; the terephthalic acid is regenerated terephthalic acid (r-PTA), and the content of p-toluic acid (p-PTA) is less than or equal to 30 ppm; the content of p-carboxybenzaldehyde (4-CBA) is less than or equal to 10 ppm. By limiting the regenerated r-PTA (p-PTA less than or equal to 30 ppm, 4-CBA less than or equal to 10 ppm) and SSP-free melt polycondensation, the risks of thermal oxidation yellowing and carboxyl end group increase of the SSP process are avoided from the source. The hindering to chain growth is reduced, and the balance between high intrinsic viscosity and low acid value of the resin is ensured without solid-phase tackifying, the product has excellent color and hydrolysis stability, and is widely suitable for optical communication and high-end engineering plastic fields.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, and in particular to a high intrinsic viscosity polybutylene terephthalate resin without solid phase thickening, its preparation method, and the product thereof. Background Technology

[0002] Polybutylene terephthalate (PBT) is an important thermoplastic engineering plastic. In high-end applications such as fiber optic loose tubes, precision electronic connectors, and high-load mechanical transmission components, PBT resin typically requires extremely high intrinsic viscosity (IV ≥ 1.20 dL / g) to ensure excellent mechanical strength and creep resistance, while also requiring extremely low terminal carboxyl group content (AV ≤ 20 mol / t) to ensure long-term hydrolytic stability under humid and hot environments. In existing technologies, the intrinsic viscosity of PBT resin prepared using conventional melt polycondensation methods is difficult to exceed 1.05 dL / g. To obtain high-viscosity products that meet the needs of high-end applications, solid-phase thickening (SSP) technology is commonly used industrially. This involves treating base chips at high temperatures (>200°C) under vacuum or inert gas flow for an extended period (20-24 hours). The existing solid-phase thickening (SSP) process has the problem of increased manufacturing costs due to prolonged high-temperature treatment. Moreover, the solid-phase reactants can only diffuse slowly inside the particles and cannot fully and uniformly contact and react. This results in some resin molecules reacting fully and having longer chains, while others react insufficiently and have shorter chains, ultimately leading to a wider molecular weight distribution (increased PDI). This causes unstable fluidity and viscosity during melt processing, which in turn affects processing stability. In addition, prolonged treatment can also cause oxidation of the resin product surface, yellowing of the color (increased b value), and the process can easily cause oxidation and dehydration of terminal hydroxyl groups, resulting in an increase in the content of terminal carboxyl groups (AV) instead of a decrease, thus reducing the long-term hydrolysis resistance of the material.

[0003] Attempting to increase the viscosity of petrochemical PBT by forcibly extending the reaction time during the melt polymerization stage without solid-phase thickening (SSP) processing will lead to severe thermal degradation of the polymer, a surge in terminal carboxyl group (AV) content, and render the product unusable. Therefore, developing a technology to directly prepare high-viscosity, low-acid-value, excellent-color, and narrow-molecular-weight distribution PBT through melt polycondensation alone, without the need for SSP processing, is a pressing problem for the industry. Summary of the Invention

[0004] To address the aforementioned shortcomings in existing production processes, the applicant provides a high-intrinsic-viscosity polybutylene terephthalate resin without solid-phase thickening, along with its preparation method and product. Using recycled terephthalic acid r-PTA as raw material, with the recycled r-PTA containing ≤30ppm p-methylbenzoic acid (p-TA) and ≤10ppm p-carboxybenzaldehyde (4-CBA), the resin product exhibits excellent processing stability, hydrolysis resistance, and color through direct melt polycondensation under the action of a catalyst, eliminating the need for solid-phase thickening.

[0005] The technical solution adopted in this invention and its beneficial effects are as follows:

[0006] This invention provides a high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening (SSP). The resin is obtained by melt polycondensation of terephthalic acid and 1,4-butanediol components without solid-phase thickening (SSP) treatment. The terephthalic acid is recycled terephthalic acid (r-PTA), with a p-methylbenzoic acid (p-TA) content ≤30ppm and a p-carboxybenzaldehyde (4-CBA) content ≤10ppm. By limiting the recycled r-PTA (p-TA ≤30ppm, 4-CBA ≤10ppm) and avoiding SSP-free melt polycondensation, the risks of thermal oxidative yellowing and increased terminal carboxyl groups associated with the SSP process are avoided from the outset. This reduces the hindrance to chain growth, ensuring that the resin achieves a balance between high intrinsic viscosity and low acid value without solid-phase thickening. The product exhibits excellent color and hydrolytic stability, making it widely applicable in optical communication and high-end engineering plastics fields. The intrinsic viscosity (IV) of the resin is ≥1.20 dL / g. The product meets the high viscosity standards required for high-end applications, satisfying the mechanical strength and creep resistance requirements of fiber optic loose tubes and high-load mechanical transmission components without the need for SSP technology, while avoiding the performance degradation caused by SSP.

[0007] The carbon isotope abundance δ¹³C value ranges from -27‰ to -24‰. The δ¹³C value provides a basis for raw material traceability, ensuring that recycled r-PTA is used.

[0008] The resin has an end carboxyl group content (AV) ≤ 20 mol / t. This effectively inhibits the catalytic sites of hydrolysis, significantly improves the product's hydrolysis resistance, and ensures that the product does not age during long-term use in humid and hot environments.

[0009] The resin has an initial hue b* value ≤ 5.0. The product has excellent hue and can meet the downstream online dyeing requirements without the need for adding colorants, thus reducing processing costs. At the same time, it avoids the influence of chromophores on the product's optical and mechanical properties, making it suitable for fields with stringent appearance requirements such as optical communication and precision electronics.

[0010] After undergoing high-pressure accelerated aging (PCT) at 121°C and 100% relative humidity for 48 hours, the resin retains ≥80% of its intrinsic viscosity. This product maintains its core performance even under harsh conditions of 121°C and saturated steam, significantly outperforming existing technologies. This ensures the product's lifespan under long-term humid and hot conditions (such as outdoor optical cables and internal components of electronic devices), expanding its adaptability to high-end application scenarios.

[0011] The molecular weight distribution index (PDI = Mw / Mn) of the resin is between 1.8 and 2.2. The narrow PDI distribution ensures uniform flowability during melt processing, avoids the problem of uneven molecular chains caused by SSP, and improves processing stability and product qualification rate.

[0012] This invention provides a method for preparing the above-mentioned high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening. After esterification, a polycondensation reaction is performed, with a polycondensation time ≤180 min. This shortens the production cycle, reduces the risk of thermal degradation, avoids increased AV and color deterioration caused by prolonged polycondensation, significantly improves production efficiency, reduces energy consumption and costs, and ensures stable product performance.

[0013] The catalyst is a titanium-based catalyst, added at a rate of 600-1000 ppm of the theoretical polymer yield. The catalyst ensures efficient chain growth in a short time, eliminating the need to extend the polycondensation time.

[0014] The final polycondensation temperature is controlled at 250-260℃, and the vacuum degree is <50Pa. The polymerization reaction conditions are optimized to promote the rapid removal of small molecule products (such as BDO); ​​at the same time, thermal oxidation and ester bond breaking caused by excessively high temperatures are avoided. Combined with vacuum degree control, polymerization can be achieved in a short time.

[0015] This invention provides a product prepared using the aforementioned solid-phase-free, high-intrinsic-viscosity polybutylene terephthalate resin. The product is used as a loose tube for optical fibers, a sheath for optical cables, a precision electronic connector, or a high-load mechanical transmission component. It precisely meets the core needs of fields such as optical communication, precision electronics, and high-load machinery, addressing the performance shortcomings of existing products in these areas, demonstrating the practical value and industrialization prospects of this invention. Detailed Implementation

[0016] The high intrinsic viscosity polybutylene terephthalate resin of the present invention, which is free from solid-phase thickening, is obtained by melt polycondensation of terephthalic acid and 1,4-butanediol. The terephthalic acid is recycled terephthalic acid (r-PTA). The recycled terephthalic acid (r-PTA) has a p-methylbenzoic acid (p-TA) content ≤30ppm, a p-carboxybenzaldehyde (4-CBA) content ≤10ppm, and its carbon isotope abundance is characterized by δ¹³C value, with a distribution range of -27‰ to -24‰.

[0017] The high intrinsic viscosity polybutylene terephthalate resin of this invention is prepared without solid-phase thickening (SSP) treatment. A titanium-based catalyst (such as tetrabutyl titanate) is used, with an addition amount of 600-1000 ppm (preferably 800 ppm) of the theoretical polymer yield. The final polycondensation temperature is controlled at 250-260℃, and the vacuum degree is <50 Pa. The intrinsic viscosity (IV) of the polybutylene terephthalate resin of this invention is ≥1.20 dL / g, and the terminal carboxyl group content (AV) is ≤20 mol / t. It can be used to prepare optical fiber loose tubes, optical cable sheaths, extruded rods, precision electronic connectors, or high-strength injection molded parts.

[0018] 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.

[0019] 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%.

[0020] Table 1:

[0021] 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-1 Comparative / Petrochemical Grade 150 25 -28.5‰

[0022] The specific testing methods are as follows (all quantitative analyses were performed in at least three parallel experiments, and the average value was taken):

[0023] 1. Intrinsic Viscosity (IV) Test Method: Refer to ISO 1628-5 or GB / T 14190-2017 for details. Use an automatic Ubbelohde viscometer and a solvent of phenol / 1,1,2,2-tetrachloroethane (1:1) dissolved at 110-120℃ for 30 minutes. Measure the outflow time in a constant temperature water bath at 25.00℃ and calculate using the Solomon-Ciuta formula.

[0024] 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.

[0025] 3. 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.

[0026] 4. 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‰.

[0027] 5. PCT Accelerated Aging Test (Hydrolysis Resistance): The sample was placed in an environment of 121℃, 100% relative humidity (saturated steam), and 2 atm pressure for 48 hours. After aging, the sample was washed with deionized water and dried in a vacuum oven at 80℃ for 12 hours to remove physically adsorbed water. The intrinsic viscosity (IV) value after aging was measured, and the retention rate was calculated.

[0028] 6. 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).

[0029] 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.

[0030] All embodiments and comparative examples of this invention were conducted in a 30L stainless steel polymerization reactor equipped with a distillation column and a high vacuum system, with a PBT product yield of 10.0 kg in each case. The raw materials were 7.55 kg of r-PTA (or v-PTA) and 7.37 kg of BDO (molar ratio 1:1.8), and the catalyst was 8.0 g (800 ppm) of TBT. No antioxidants or colorants were added in any of the examples to accurately reflect the resin characteristics. The specific process flow was as follows: esterification was first carried out at 230°C and atmospheric pressure until water was discharged; then the temperature was raised to 255°C, and the vacuum was reduced to <50 Pa within 30 minutes to carry out polycondensation. The reaction endpoint was determined by the stirring power (torque), and the material was immediately discharged and pelletized upon reaching the target.

[0031] Example 1: Using r-PTA-1 from Table 1 as raw material, the material was discharged directly after polycondensation for 150 minutes, with IV 1.32 dl / g and PDI = 2.05.

[0032] Example 2: Using r-PTA-2 from Table 1 as raw material, the material was directly discharged after polycondensation for 170 minutes, with IV 1.27 dl / g and PDI = 2.12. The remaining steps were the same as in Example 1.

[0033] Example 3: Using r-PTA-1 from Table 1 as raw material, the product was directly discharged after polycondensation for 180 minutes, with IV 1.36 dl / g and PDI = 2.10. The remaining steps were the same as in Example 1.

[0034] Comparative Example 1:

[0035] Using v-PTA-1 from Table 1 as the raw material, the polymerization time was extended to 190 minutes in order to forcefully achieve a high viscosity. The melt had a distinctly pungent odor upon discharge.

[0036] Comparative Example 2:

[0037] Using v-PTA-1 from Table 1 as raw material, basic slices were obtained after polycondensation for 140 minutes. The prepared basic slices (IV value of 1.02 dl / g) were placed in a solid-phase polycondensation reactor and subjected to SSP treatment at 205°C under nitrogen flow for 24 hours to increase the intrinsic viscosity to 1.32 dl / g and broaden the PDI to 2.35.

[0038] Comparative Example 3: Using r-PTA-1 from Table 1 as raw material, basic slices were obtained after polycondensation for 120 minutes. The prepared basic slices were placed in a solid-phase polycondensation reactor and subjected to SSP treatment for 18 hours under a nitrogen flow at 205°C.

[0039] The final PBT product was tested using the above method, and the physical properties are shown in Table 2.

[0040] Table 2:

[0041] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 feature Basic Implementation Wide range Extremely high viscosity Petrochemical direct melt polymerization Petrochemical + SSP r-PTA-1+SSP Raw material type r-PTA-1 r-PTA-2 r-PTA-1 v-PTA-1 v-PTA-1 r-PTA-1 Condensation time 150min 170min 180min 190min 140min+24hSSP 120min+18hSSP Intrinsic viscosity IV (dl / g) 1.32 1.27 1.36 1.31 1.32 1.32 Terminal carboxyl group AV (mol / t) 15.5 18.0 19.5 31.0 15.2 11.4 PDI distribution 2.05 2.12 2.10 2.25 2.35 2.21 * 3.8 4.8 3.5 6.1 6.5 5.1 PCT retention rate 88% 82% 85% 51% 78% 90%

[0042] The PDI values ​​show that the molecular weight distribution of the PBT resin obtained by the present invention is narrower, indicating that Examples 1 to 4 of the present invention were not treated with SSP.

[0043] Comparing Example 1 with Comparative Example 1, both examples employed a direct melt polymerization process. Example 1 used ultra-low p-TA (12 ppm) and 4-CBA (2.5 ppm) r-PTA raw materials, achieving an IV of 1.32 dl / g and an AV of only 15.5 mol / t within 150 minutes. Comparative Example 1, with its high p-TA (150 ppm) and 4-CBA (25 ppm) raw materials, experienced hindered chain growth, forcing a prolonged reaction time of 190 minutes. Increasing the polycondensation time led to severe thermal degradation, ester bond breakage, and the generation of numerous terminal carboxyl groups, causing the AV to surge to 31.0 mol / t. Simultaneously, the small molecules generated by degradation triggered secondary side reactions, exacerbating the heterogeneity of molecular chain breakage and increasing the PDI to 2.25. The high acid value catalyzed the hydrolysis reaction, accelerating ester bond breakage in the PCT aging environment, resulting in a PCT retention rate of only 51% and severe aging. In contrast, Example 1's short polycondensation time reduced thermal degradation, resulting in a lower AV value and significantly superior hydrolytic stability.

[0044] Comparing Example 1 with Comparative Example 2, although Comparative Example 2 achieved high viscosity, due to the inhomogeneity of the solid-phase reaction, the resin was in a solid particle state during the solid-phase thickening process, and the movement of molecular chain segments was restricted. The residual 1,4-butanediol (BDO) and oligomers could only diffuse slowly inside the particles. This led to the easy volatilization or reaction of low-molecular-weight substances on the particle surface, resulting in more complete chain growth; while diffusion inside the particles was hindered, and the reaction was incomplete, ultimately forming a heterogeneous structure with long chains on the surface and short chains inside. This widened the PDI to 2.35, resulting in a large difference in molecular size, poor dispersibility and purity of polymer molecules, and the 24-hour baking caused the resin to yellow (b*6.5) (the high-temperature environment triggered an oxidation reaction of the resin molecular chains). Because Example 1 of this invention is a homogeneous melt polymerization, the system is in a homogeneous state, the monomers, oligomers and catalyst are in uniform contact, the growth rate of all molecular chains is consistent, the PDI is kept in a narrow range of 2.05, and thermal history is avoided. The b value is only 3.8*, avoiding the risk of thermal oxidation yellowing and acid value increase caused by SSP, and achieving better melt processing stability and hydrolysis resistance (PCT88%).

[0045] Comparing Example 1 with Comparative Example 3, Comparative Example 3 used r-PTA-1 as a raw material and underwent solid-state polycondensation, resulting in a PBT resin with a faster polymerization rate than Comparative Example 2, and also yielded a lower end carboxyl value (AV only 11.4 mol / t). However, Example 1 had a better hue value, while Comparative Example 3 had a hue value as high as 5.1. This shows that the hue deteriorates after SSP (solid-state polycondensation). This invention eliminates the SSP step, completing chain growth solely through melt homogeneous polymerization, resulting in a shorter thermal history and suppressed oxidation reaction, thus producing a product with excellent hue. Downstream fiber optic loose tube customers can directly dye the product online, reducing toner costs.

[0046] Comparing Example 3 with Comparative Example 1, Example 3, using r-PTA-1 as raw material without solid-state polycondensation, can increase the intrinsic viscosity IV to 1.36 dl / g, while Comparative Example 1, without solid-state polycondensation, can only achieve a maximum viscosity of 1.31 dl / g.

[0047] Comparing the examples with the comparative examples, it can be determined that by selecting raw materials with p-methylbenzoic acid (p-TA) content ≤30ppm and p-carboxybenzaldehyde (4-CBA) content ≤10ppm, PBT products with high viscosity, low acid value, narrow molecular weight distribution, good processing stability, and excellent hydrolysis resistance can be obtained without solid-state polycondensation. The polycondensation time of Examples 1-3 is only 150-180 minutes, eliminating the need for subsequent solid-state thickening steps, and the entire production cycle is ≤180 minutes. Furthermore, the examples do not require antioxidants or colorants, further saving raw material costs. In addition, the PDI of the examples is 2.05-2.12, with uniform molecular chain length and stable melt flow. This can avoid wall thickness deviations and surface defects caused by uneven molecular chains during fiber optic loose tube extrusion and precision electronic connector injection molding.

[0048] 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 intrinsic viscosity polybutylene terephthalate resin that does not require solid-phase thickening, characterized in that: The resin is obtained by melt polycondensation of terephthalic acid and 1,4-butanediol components, and has not undergone solid-phase thickening (SSP) treatment; the terephthalic acid is regenerated terephthalic acid (r-PTA), and the p-methylbenzoic acid (p-TA) content is ≤30ppm; the p-carboxybenzaldehyde (4-CBA) content is ≤10ppm; the intrinsic viscosity (IV) of the resin is ≥1.20dL / g; and the carbon isotope abundance δ¹³C value distribution ranges from -27‰ to -24‰.

2. The high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening according to claim 1, characterized in that: The end carboxyl group content (AV) of the polybutylene terephthalate resin is ≤20mol / t.

3. The high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening according to claim 1, characterized in that: The initial hue b* value of the polybutylene terephthalate resin is ≤5.

0.

4. The high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening according to claim 1, characterized in that: After the polybutylene terephthalate resin is subjected to high-pressure accelerated aging (PCT) at 121°C and 100% relative humidity for 48 hours, its intrinsic viscosity retention rate is ≥80%.

5. The high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening according to claim 1, characterized in that: The molecular weight distribution index (PDI = Mw / Mn) of the polybutylene terephthalate resin is 1.8 to 2.

2.

6. A method for preparing the high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening as described in any one of claims 1-5, characterized in that: After the esterification reaction is completed, a polycondensation reaction is carried out, and the polycondensation time is ≤180min.

7. The method for preparing the high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening according to claim 6, characterized in that: The catalyst is a titanium-based catalyst, and the addition amount is 600-1000 ppm of the theoretical polymer yield.

8. The method for preparing the high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening according to claim 6, characterized in that: The final polycondensation temperature is controlled at 250-260℃, and the vacuum degree is <50Pa.

9. A product prepared using the high intrinsic viscosity polybutylene terephthalate resin without solid-phase thickening as described in any one of claims 1 to 5, characterized in that: The products are fiber optic loose tubes, optical cable sheaths, precision electronic connectors, or high-load mechanical transmission components.