High-temperature-resistant polyester filament and preparation method thereof

Abstract

The present application belongs to the technical field of chemical fiber manufacturing, and particularly relates to a high-temperature-resistant polyester filament and a preparation method thereof. The preparation method comprises the following steps: melt blending raw materials including polyethylene terephthalate chips, polyimide powder and surface-modified diatomite to prepare a composite master batch, and then melt spinning the composite master batch to prepare the high-temperature-resistant polyester filament; the preparation process of the surface-modified diatomite comprises the following steps: firstly, calcining diatomite powder, and then modifying the diatomite powder with a silane coupling agent; the polyimide powder and the surface-modified diatomite construct a double high-temperature-resistant network structure in the high-temperature-resistant polyester filament. The prepared high-temperature-resistant polyester filament is not prone to shrinkage and deformation in a high-temperature environment, has excellent size stability and mechanical properties, is suitable for high-temperature filtration, heat protective clothing and other application scenarios with high requirements for the thermal stability of fibers, and can further take into account the flame retardance and ultraviolet aging resistance on this basis.

Description

Technical Field

[0001] This invention belongs to the field of chemical fiber manufacturing technology, specifically relating to a high-temperature resistant polyester filament and its preparation method. Background Technology

[0002] Currently widely used ordinary polyester filaments have limited heat resistance. When working in high-temperature environments for a long time, they are prone to softening, deformation, and significant decrease in strength, making it difficult to meet the needs of special industrial fields such as high-temperature filtration and thermal protective clothing. Furthermore, these polyester filaments have a low limiting oxygen index and high flammability, posing safety hazards in situations involving open flames or high-temperature heat sources. Moreover, their molecular structure is relatively sensitive to ultraviolet light, and long-term exposure to outdoor sunlight can easily lead to photo-oxidative aging, causing molecular chain breakage, resulting in reduced fiber strength, yellowing, and shortened service life.

[0003] To address the above problems, some improvements have been attempted in the existing technology, but the following shortcomings still exist:

[0004] (1) Limited improvement in high-temperature resistance. The long-term service temperature of conventional polyester filament is usually only around 130~150℃. Although existing modification technologies have made some improvements, it is still difficult to make the fiber work stably for a long time above 200℃. The strength retention rate and dimensional stability at high temperatures are insufficient. For example, patent application CN120905796A discloses a wear-resistant and high-temperature resistant polyester fiber and its preparation method. It uses carboxylated carbon nanotubes to modify PET for melt spinning, which improves the high-temperature resistance of polyester fiber to a certain extent. However, its modification scheme is mainly based on the single reinforcing component route of carbon nanotubes. The improvement in the long-term service temperature of the fiber is limited. It still faces the problem of insufficient strength retention rate and dimensional stability at high temperatures above 200℃.

[0005] (2) The flame retardant modification effect is not good. Although there are existing technologies that use flame retardants such as nano-sized magnesium hydroxide, under conventional addition dosage and method, flame retardants are prone to uneven dispersion, poor compatibility with polyester matrix, and failure at high temperature, making it difficult to obtain the ideal flame retardant level while ensuring spinnability.

[0006] (3) Weak resistance to UV aging. Although there are solutions in the existing technology that add UV absorbers, under normal dosage, UV absorbers are prone to sublimation and migration during high-temperature processing and use, and the UV resistance effect decays rapidly over time, making it difficult to meet the durability requirements for long-term outdoor use.

[0007] Therefore, there is an urgent need to develop a polyester filament and its preparation method that can improve high temperature resistance and further take into account flame retardancy and UV aging resistance. Summary of the Invention

[0008] The purpose of this invention is to solve the problems in the prior art and provide a high-temperature resistant polyester filament and its preparation method.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing high-temperature resistant polyester filament involves melt-blending raw materials including polyethylene terephthalate (PET) chips, polyimide powder, and surface-modified diatomaceous earth to obtain a composite masterbatch, and then melt-spinning the composite masterbatch to obtain high-temperature resistant polyester filament.

[0011] The preparation process of surface-modified diatomaceous earth includes: first, calcining the diatomaceous earth powder, and then modifying it with a silane coupling agent;

[0012] The silane coupling agent is selected from one of KH-550, KH-560, and KH-570;

[0013] Polyimide powder and surface-modified diatomaceous earth are used to construct a dual high-temperature resistant network structure in high-temperature resistant polyester filaments.

[0014] The preparation principle of the surface-modified diatomaceous earth of the present invention is as follows:

[0015] First, through calcination, organic impurities and bound water in diatomaceous earth are removed, and the pore structure in diatomaceous earth is optimized, making the originally blocked and obstructed pores open, clean and usable, fully exposing the hydroxyl active sites on its outer surface and the inner wall of the pores, providing sufficient reaction sites for subsequent coupling agent grafting.

[0016] Subsequently, a condensation reaction is carried out between a silane coupling agent (such as one with amino or other functional groups) and the aforementioned hydroxyl groups to form a stable chemical bond. Organic segments with good compatibility with the PET matrix are introduced into the outer surface of the diatomaceous earth and the inner wall of the pores, thereby achieving a strong interfacial bond between the surface-modified diatomaceous earth and the PET matrix, rather than a simple physical filling.

[0017] The construction principle of the dual high-temperature resistant network structure of the present invention is as follows:

[0018] ① The role of surface-modified diatomaceous earth: Surface-modified diatomaceous earth is uniformly dispersed in the PET matrix and forms a physical rigid skeleton through strong interfacial bonding. Like "steel bars", it restricts the slippage and deformation of PET molecular chains at high temperatures and ensures the dimensional stability of the fibers.

[0019] ② The role of polyimide powder: Polyimide molecular chains have a rigid structure of aromatic ring conjugation, which can be interwoven between PET molecular chains to form a rigid molecular network, increase the thermal decomposition temperature of PET matrix, and inhibit the thermo-oxidative degradation of molecular chains at high temperature.

[0020] ③ Synergistic Mechanism: The physical rigid framework of surface-modified diatomaceous earth and the molecular rigid network of polyimide intertwine and support each other. The diatomaceous earth framework provides dispersion support sites for polyimide, preventing its aggregation; the polyimide network fills the gaps in the diatomaceous earth framework, avoiding high-temperature stress concentration and cracking. Through the combination of micron-scale physical rigidity and molecular-scale chemical rigidity, the two form a dual high-temperature resistant network structure of "physical + chemical," achieving a synergistic enhancement effect and providing comprehensive high-temperature resistance enhancement to the PET matrix from macroscopic to microscopic levels.

[0021] Furthermore, the technical advantage of the process steps of this invention lies in the following: first, a composite masterbatch is prepared by melt blending, which fully and uniformly disperses the PET chips, surface-modified diatomaceous earth, and polyimide powder, before melt spinning. This "two-step" spinning process ensures the uniform distribution of each component in the fiber, avoiding problems such as uneven dispersion and filter clogging that may occur with direct spinning.

[0022] As a preferred technical solution:

[0023] The method for preparing high-temperature resistant polyester filament as described above includes a calcination process in which diatomaceous earth powder is heated to 500-600°C at a heating rate of 3-5°C / min and calcined for 2-4 hours. By using this heating rate, temperature, and time parameters, it is possible to effectively remove organic impurities and bound water, clear pores, and expose hydroxyl groups, while further suppressing excessive damage to the pore structure and excessive condensation of hydroxyl groups that may be caused by excessively rapid heating or excessively high temperatures. This better preserves the specific surface area and active site distribution of diatomaceous earth, providing a better reaction interface for subsequent silane coupling agent grafting.

[0024] The method for preparing high-temperature resistant polyester filament as described above, wherein the silane coupling agent modification process is as follows: calcined diatomaceous earth powder, silane coupling agent, ethanol and water are mixed and reacted at 70~80℃ for 2~3 hours, wherein the mass of silane coupling agent accounts for 3%~5% of the mass of calcined diatomaceous earth powder, and the mass ratio of silane coupling agent, ethanol and water is 1:6:3.

[0025] The reaction temperature and reaction time ensure that the grafting reaction proceeds fully while effectively suppressing the self-polymerization side reaction of the silane coupling agent, further ensuring the uniformity of grafting.

[0026] The dosage of this silane coupling agent can further achieve an ideal coverage state close to a monolayer while ensuring effective modification of the outer surface and inner wall of the pores of diatomite, thereby achieving a better balance between grafting efficiency and pore unobstructedness.

[0027] Taking KH-550 as an example, the terminal functional groups of KH-550 include primary amino groups, which are more conducive to undergo amidation reaction with ester groups in PET molecular chains under high temperature melt spinning to form covalent bonds. At the same time, hydrogen bonding is also used to achieve strong chemical affinity between diatomite and PET, thereby further enhancing the interfacial bonding strength.

[0028] The preparation method of the high-temperature resistant polyester filament described above further includes: post-treatment after silane coupling agent modification.

[0029] The post-treatment involves sequentially filtering, washing (e.g., washing 2-3 times with deionized water, then 2-3 times with anhydrous ethanol), drying (e.g., drying the washed filter cake for 4-6 hours under a vacuum of less than -0.08 MPa and a temperature of 100-120°C), and pulverizing and sieving (e.g., passing it through a 400-500 mesh sieve).

[0030] This post-treatment process, through filtration and washing, can more quickly and effectively remove unreacted silane coupling agents and byproducts, ensuring the purity and cleanliness of the surface-modified diatomaceous earth. At the same time, drying further removes residual moisture, preventing hydrolytic degradation of PET in subsequent processing. After crushing and sieving, finer and more uniformly distributed powder is obtained, thereby further improving its dispersion uniformity in the PET matrix and providing better raw material quality assurance for the subsequent two-step spinning process.

[0031] The method for preparing high-temperature resistant polyester filament as described above, by weight, comprises 50-70 parts polyethylene terephthalate (PET) chips, 5-10 parts surface-modified diatomaceous earth, and 8-12 parts polyimide powder; PET chips are used as the matrix material, and this amount of PET chips ensures sufficient melt flowability and spinnability during fiber forming, avoiding a sudden increase in melt viscosity, increased filtration pressure, and spinning difficulties caused by excessive fillers such as surface-modified diatomaceous earth and polyimide; the surface-modified diatomaceous earth is used in a proportion of 5-10 parts. The amount of polyimide forms a continuous physical rigid skeleton, while the amount of polyimide at 8-12 parts constructs a through-through molecular rigid network. The two are matched in proportion to achieve the optimal synergistic enhancement of the dual high-temperature resistant network structure of "physical + chemical". At the same time, the total amount of fillers such as surface-modified diatomaceous earth and polyimide is controlled at 13-22 parts, which further avoids the problems of uneven dispersion, filter clogging and reduced spinnability caused by excessive amounts of these fillers. It also better balances material cost while significantly improving the high-temperature resistance of the fiber.

[0032] The method for preparing high-temperature resistant polyester filament as described above includes a compatibilizer (e.g., maleic anhydride-grafted polyethylene, maleic anhydride-grafted polyolefin elastomer), an antioxidant (e.g., antioxidant 168, antioxidant 1010, antioxidant 1076), and a lubricant (e.g., ethylene bis-stearamide) in the raw materials. By weight, the compatibilizer is 4-8 parts, the antioxidant is 2-4 parts, and the lubricant is 1-3 parts. The compatibilizer further improves the interfacial compatibility between PET and polyimide and surface-modified diatomaceous earth, the antioxidant further inhibits thermo-oxidative degradation during high-temperature processing, and the lubricant further reduces melt viscosity and improves fluidity. The combined effect of these three agents makes the components more uniformly dispersed, the processing more stable, and the fiber's mechanical properties and high-temperature resistance properties better overall.

[0033] Polyethylene terephthalate (PET) chips are premixed with compatibilizers, antioxidants, and lubricants to obtain a premix. This premix is ​​then melt-blended with surface-modified diatomaceous earth and polyimide powder. This premixing followed by melt-blending process allows the compatibilizers, antioxidants, and lubricants to be preferentially and uniformly dispersed within the PET matrix. This avoids competitive adsorption of these additives onto the active surfaces of the surface-modified diatomaceous earth and polyimide powder, thus ensuring both the antioxidant and lubricating effects of the additives and a strong interfacial chemical bond between the fillers and PET. This maximizes both the functionality of the additives and the reinforcement of the fillers.

[0034] The method for preparing high-temperature resistant polyester filament as described above further includes flame retardants (e.g., nano-sized magnesium hydroxide) and ultraviolet absorbers (e.g., UV-531, UV-326, UV-329) in the raw materials; by weight, the flame retardant is 10-20 parts and the ultraviolet absorber is 3-6 parts; when the raw materials simultaneously include compatibilizers, antioxidants, lubricants, flame retardants, and ultraviolet absorbers, The physical rigid framework of surface-modified diatomaceous earth provides dispersion support sites for flame retardants, inhibiting their aggregation. Compatibilizers improve the interfacial compatibility between flame retardants and the PET matrix, also inhibiting their aggregation. The porous structure of surface-modified diatomaceous earth provides uniform dispersion support sites for UV absorbers, preventing their aggregation and migration, ensuring UV absorption efficiency, and inhibiting photo-oxidative degradation of fibers during outdoor use. Therefore, flame retardants and UV absorbers enable fibers to maintain excellent high-temperature resistance while also achieving excellent flame retardant and UV resistance, expanding their application adaptability in harsh environments such as high temperatures and outdoor settings.

[0035] The premix is ​​melt-blended with surface-modified diatomaceous earth, polyimide powder, flame retardant, and UV absorber. This allows the compatibilizer, antioxidant, and lubricant to be preferentially anchored within the PET matrix, effectively preventing the physical adsorption of the flame retardant to the aforementioned additives due to its high specific surface area. At the same time, it effectively avoids competitive dispersion and intermolecular interference between the UV absorber and the additives, preventing a decrease in the effective concentration of the aforementioned additives in the PET matrix. This, in turn, ensures the thermal stability of the antioxidant, the flowability improvement of the lubricant, and the interfacial compatibilization function of the compatibilizer, achieving a synergistic coexistence of additive functions and filler enhancement.

[0036] As described above, the preparation method of high-temperature resistant polyester filament can be carried out by melt blending using a twin-screw extruder. The process parameters for melt blending are as follows: zone 1 temperature 240~250℃, zone 2 temperature 255~265℃, zone 3 temperature 265~275℃, zone 4 temperature 270~280℃, die head temperature 270~275℃, screw speed 200~300 rpm, and melt residence time 2~4 minutes.

[0037] Melt spinning includes the following steps:

[0038] The composite masterbatch is dried at 120~130℃ (for example, the drying time is 3~5 hours, so that the moisture content of the composite masterbatch is reduced to below 0.02wt%), then melted at 285~295℃ and extruded through a spinneret to form nascent fibers.

[0039] After the nascent fibers are cooled and solidified, they are subjected to two stages of hot stretching to obtain stretched fibers. The first stage of stretching is carried out in a hot water bath at a temperature of 80~90℃ and a stretching ratio of 1.5~2.0. The second stage of stretching is carried out on a hot roller at a surface temperature of 130~150℃ and a stretching ratio of 2.5~3.1.

[0040] The drawn fibers are subjected to relaxation heat setting at 180~200℃, and the running time of the drawn fibers in the relaxation heat setting zone is 1~3 minutes.

[0041] This melt spinning process avoids high-temperature hydrolysis of PET by first drying it to a moisture content of less than 0.02 wt%, and then melt extruding it at 285~295℃. Combined with two-stage gradient stretching (hot water bath + hot roller, total ratio 4.0~5.5) and relaxation heat setting at 180~200℃, the fiber achieves full orientation and crystallization, further reducing internal stress and heat shrinkage, thereby better ensuring the mechanical properties and high-temperature dimensional stability of the fiber.

[0042] The method for preparing a high-temperature resistant polyester filament as described above further includes plasma treatment of the surface of the drawn fiber after two-stage hot stretching and before relaxation heat setting.

[0043] The plasma treatment power is 200~400W, and the plasma treatment time is 0.5~2.0 seconds;

[0044] The working medium for plasma treatment is a mixture of argon and oxygen, with argon comprising 80% to 90% of the volume of the mixture.

[0045] The unique features of the aforementioned plasma treatment are: precise timing of the treatment (completed online on a high-speed winding production line after two stages of thermal stretching and before relaxation heat setting, for example, at a winding speed of 2800~3200 m / min) and targeted optimization of process parameters (power 200~400W, time 0.5~2.0 seconds, argon and oxygen mixed gas). This treatment can achieve instant activation of the fiber surface without damaging the fiber's intrinsic properties, introducing polar groups and forming a micro-nano rough structure. This results in a synergistic enhancement effect between the fiber surface and the polyimide molecular network and surface-modified diatomaceous earth rigid skeleton already constructed within the material, significantly improving the durability of high-temperature resistance, flame retardancy, and UV resistance.

[0046] The present invention also provides a high-temperature resistant polyester filament, which is prepared by the method for preparing a high-temperature resistant polyester filament as described in any of the preceding claims;

[0047] The high-temperature resistant polyester filament has a breaking strength of 6.82~8.13 cN / dtex, a breaking elongation of 15.41%~23.85%, a dry heat shrinkage rate of 2.24%~4.25% under the conditions of 180℃, 30 minutes, and 0.01 cN / dtex pretension, a thermal decomposition temperature of 441.9~457.3℃ based on 5wt% thermogravimetric analysis, a limiting oxygen index (LOI) of 30.6%~34.8%, an ultraviolet protection factor (UPF) of 54.9~67.9, and a breaking strength retention rate of 80.3%~92.6% after 300 hours of accelerated ultraviolet aging (wherein, the 300-hour accelerated ultraviolet aging was carried out in accordance with GB / T 31899-2015, and the breaking strength retention rate was tested in accordance with GB / T 14344-2022).

[0048] The dry heat shrinkage rate of ordinary polyester filament under the conditions of 180℃, 30 minutes and 0.01cN / dtex pretension is usually 8%~12%, while the present invention reduces it to 2.24%~4.25%, indicating that the fiber is not easily deformed and shrunken at high temperature and has excellent dimensional stability.

[0049] The thermal decomposition temperature of ordinary polyester filament, calculated based on 5wt% loss, is typically 400℃~420℃. This invention raises it to 441.9~457.3℃, indicating that the fiber needs to be thermally decomposed at a higher temperature and can withstand more severe thermal environments.

[0050] The dry heat shrinkage rate and thermal decomposition temperature both prove that the high-temperature resistant polyester filament prepared by this invention has achieved high temperature resistance above 200℃, meeting the needs of high-end applications such as high-temperature filtration / thermal protection clothing.

[0051] Meanwhile, the high-temperature resistant polyester filament prepared by this invention also has excellent mechanical properties as well as certain flame retardant and UV resistant properties.

[0052] Beneficial effects:

[0053] (1) The preparation method of the present invention introduces surface-modified diatomite and polyimide powder into the PET matrix at the same time. During the melt blending and melt spinning process, the two work together to construct a dual high-temperature resistant network structure of "physical rigid skeleton + molecular rigid network". At the same time, the surface-modified diatomite and the PET matrix form strong chemical bonds and good compatibility, which ensures the effectiveness of the interfacial bonding force at high temperature. This ensures that the dual high-temperature resistant network structure continues to play a reinforcing role in relaxation heat setting and subsequent high-temperature applications, and achieves all-round high-temperature resistance enhancement of the PET matrix from micro to macro.

[0054] (2) Thanks to the above-mentioned dual high temperature resistant network structure, the polyester filament prepared by the present invention is not easy to shrink and deform in high temperature environment, and can maintain high breaking strength. It has excellent dimensional stability and mechanical property retention rate, and is suitable for application scenarios with stringent requirements for fiber thermal stability, such as high temperature filtration and thermal protective clothing.

[0055] (3) The preparation method of the present invention adopts a two-step process of first melting and blending to form a composite masterbatch and then melting and spinning, so that each component is fully and uniformly dispersed in the masterbatch, avoiding problems such as uneven dispersion and filter clogging that may occur in direct spinning, and ensuring the stability of the spinning process and the uniformity of fiber quality.

[0056] (4) When the raw materials of the present invention further include flame retardants and ultraviolet absorbers, due to the synergistic dispersion of flame retardants and surface-modified diatomite rigid skeleton, and the anchoring effect of ultraviolet absorbers in the porous structure of diatomite, the high-temperature resistant polyester filaments obtained also have good flame retardant properties and long-lasting anti-ultraviolet aging properties, further expanding their application adaptability in harsh environments. Detailed Implementation

[0057] 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.

[0058] (1) Fracture strength: Fracture strength is calculated according to the formula Fracture strength = Fracture force / Linear density. The unit of fracture strength is cN / dtex.

[0059] The breaking strength was tested according to GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments". Specifically, an Instron 3344 constant speed elongation electronic tensile testing machine was used with a clamping distance of 500 mm and a tensile speed of 500 mm / min. The pre-tension was applied at 0.05 cN / dtex. The sample was conditioned for 24 hours at a temperature of 20±2℃ and a relative humidity of 65±4% before testing. The arithmetic mean of three parallel tests was taken as the final result of the breaking strength, in cN.

[0060] Linear density was tested according to GB / T 14343-2008 "Test Method for Linear Density of Chemical Fiber Filaments". The arithmetic mean of three parallel tests was taken as the final result of linear density, and the unit is dtex.

[0061] (2) Elongation at break: The test was conducted in accordance with GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments". Specifically, an Instron 3344 constant speed elongation electronic tensile testing machine was used, with a clamping distance of 500 mm, a tensile speed of 500 mm / min, and a pre-tension of 0.05 cN / dtex. The sample was conditioned for 24 hours at a temperature of 20±2℃ and a relative humidity of 65±4% before the test. The elongation (in mm) between the marks at the time of breakage was read from the tensile strength-elongation curve, and the elongation at break was calculated using the following formula:

[0062] Elongation at break = (Elongation between markings at break / Initial distance between markings) × 100%;

[0063] In the formula, the initial distance between the markings is the clamping distance, which is 500mm;

[0064] The arithmetic mean of three parallel tests was taken as the final result of the elongation at break.

[0065] (3) Dry heat shrinkage rate: Referring to the single-filament method in GB / T 6505-2017 "Test Method for Heat Shrinkage Rate of Chemical Fiber Filaments (After Treatment)", the heat shrinkage tester (LENZING TST510) was used to test the filaments at 180℃ for 30 minutes under a pretension of 0.01cN / dtex. A total of 10 filaments were tested, and each filament was tested 5 times. The arithmetic mean of all test data was taken as the final result for the 10 filaments.

[0066] (4) Thermal decomposition temperature based on 5wt% thermogravimetric analysis: The test was conducted in accordance with GB / T 37631-2019 "Test Method for Thermal Decomposition Temperature of Chemical Fibers". Specifically, a thermogravimetric analyzer (TA Instruments TGA 5500) was used. (5±1) mg of sample was weighed and heated from room temperature (25℃) to 800℃ at a heating rate of 10℃ / min under a nitrogen atmosphere with a gas flow rate of 50 mL / min. The mass change curve with temperature (TG curve) was recorded. The temperature corresponding to the mass loss of 5wt% was read from the curve, which is the thermal decomposition temperature based on 5wt% thermogravimetric analysis.

[0067] (5) Limiting oxygen index: The test was conducted in accordance with FZ / T 50017-2011 "Test method for flame retardant properties of polyester fiber: oxygen index method".

[0068] (6) Ultraviolet Protection Coefficient: First, the polyester filament to be tested was made into a fabric. The fabric adopted a plain weave structure with a warp density of 400 threads / 10cm and a weft density of 320 threads / 10cm. Both the warp and weft yarns used were made of the polyester filament to be tested. Then, the ultraviolet protection coefficient of the fabric was tested according to GB / T 18830-2009 "Evaluation of Ultraviolet Protection Performance of Textiles". Specifically, an ultraviolet-visible spectrophotometer (Hitachi U-4100 model, with integrating sphere accessory) was used to measure the spectral transmittance in the wavelength range of 280~400 nm and calculate the ultraviolet protection coefficient. Four samples were taken for each type of fabric, and the arithmetic mean was taken as the final ultraviolet protection coefficient.

[0069] (7) Fracture strength retention rate after 300 hours of UV accelerated aging: UV accelerated aging for 300 hours was carried out in accordance with GB / T31899-2015, and fracture strength retention rate was tested in accordance with GB / T 14344-2022.

[0070] Example 1

[0071] A method for preparing high-temperature resistant polyester filament, the specific steps of which are as follows:

[0072] (1) Raw material preparation

[0073] Polyethylene terephthalate (PET) slices: The intrinsic viscosity of polyethylene terephthalate is 1.12 dL / g. This intrinsic viscosity was determined using the capillary viscometer method according to GB / T 14190-2017. The length, width, and height of the slices are 4 mm, 5 mm, and 2.5 mm, respectively.

[0074] Polyimide powder: average particle size 30μm, glass transition temperature ≥260℃ (determined by DSC method, referring to GB / T19466.2-2004), thermal decomposition temperature ≥500℃ based on 5wt% thermogravimetric analysis, density 1.3g / cm³, manufacturer: Shandong Kesim Special Materials Development Co., Ltd., grade: KSM-PI-30;

[0075] Diatomaceous earth powder: SiO2 mass fraction ≥85%, manufacturer is Linjiang City Dayuan Diatomaceous Earth New Material Ecological and Environmental Protection Technology Co., Ltd., grade is DZ300;

[0076] Silane coupling agent: KH-550, CAS No. 919-30-2, purity ≥98%;

[0077] Deionized water;

[0078] Anhydrous ethanol;

[0079] Compatibilizer: Maleic anhydride grafted polyolefin elastomer (MAH-g-POE), manufactured by Wuhan Jiyesheng Chemical Co., Ltd., brand name A00856;

[0080] Antioxidant: Antioxidant 168, manufactured by BASF, brand name Irgafos 168;

[0081] Lubricant: Ethylene bis-stearamide, manufactured by CMS Chemical Industries, Indonesia, brand name HI-LUBP-200;

[0082] Flame retardant: Nano-sized magnesium hydroxide with an average particle size of 50nm, manufactured by Liaoning Jinghua New Material Co., Ltd., brand name JH-MH-50;

[0083] Ultraviolet absorber: UV-531, CAS No. 1843-05-6, purity ≥99.0%;

[0084] (2) Preparation of surface-modified diatomaceous earth

[0085] (2.1) Calcination treatment: The diatomaceous earth powder was heated to 500℃ at a heating rate of 3℃ / min and calcined for 2 hours;

[0086] (2.2) Modification treatment: The calcined diatomaceous earth powder, silane coupling agent, ethanol and water are mixed and reacted at 70°C for 2 hours. The mass of the silane coupling agent accounts for 3% of the mass of the calcined diatomaceous earth powder, and the mass ratio of silane coupling agent, ethanol and water is 1:6:3.

[0087] (2.3) Post-processing: The material modified by silane coupling agent is sequentially filtered, washed, dried, crushed and sieved to obtain surface-modified diatomaceous earth.

[0088] The washing process involves first washing twice with deionized water, and then washing twice with anhydrous ethanol.

[0089] Drying involves drying the washed filter cake under a vacuum of -0.085 MPa and a temperature of 100°C for 4 hours.

[0090] The grinding and sieving process involves passing the material through a 400-mesh sieve.

[0091] (3) Melt blending

[0092] (3.1) Polyethylene terephthalate chips are premixed with compatibilizer, antioxidant and lubricant to obtain a premix;

[0093] (3.2) The premix was melt-blended with surface-modified diatomaceous earth, polyimide powder, flame retardant and ultraviolet absorber to obtain composite masterbatch;

[0094] By weight, the following components are present: 50 parts polyethylene terephthalate chips, 10 parts surface-modified diatomaceous earth, 12 parts polyimide powder, 8 parts compatibilizer, 4 parts antioxidant, 3 parts lubricant, 20 parts flame retardant, and 6 parts ultraviolet absorber.

[0095] Melt blending was carried out using a twin-screw extruder. The process parameters for melt blending were: zone 1 temperature 240℃, zone 2 temperature 255℃, zone 3 temperature 265℃, zone 4 temperature 270℃, die head temperature 270℃, screw speed 200 rpm, and melt residence time 4 minutes.

[0096] (4) Melt spinning

[0097] (4.1) The composite masterbatch is dried at 120°C for 5 hours to reduce the moisture content of the composite masterbatch to below 0.02wt%, and then melted at 285°C. The masterbatch is then extruded through a spinneret to form nascent fibers. The spinneret has circular spinneret holes with an outlet diameter of 0.3mm.

[0098] (4.2) After the nascent fiber is cooled and solidified, it is subjected to two-stage hot stretching to obtain stretched fiber. The first stage of stretching is carried out in a hot water bath at a water temperature of 80℃ and a stretching ratio of 1.5. The second stage of stretching is carried out on a hot roller at a roller surface temperature of 130℃ and a stretching ratio of 2.5.

[0099] (4.3) Plasma treatment of the surface of the drawn fibers

[0100] The plasma treatment power is 200W, and the plasma treatment time is 2.0 seconds;

[0101] The working medium for plasma treatment is a mixture of argon and oxygen, with argon comprising 80% of the volume in the mixture.

[0102] (4.4) The plasma-treated drawn fiber is subjected to relaxation heat setting at 180°C. The running time of the drawn fiber in the relaxation heat setting zone is 3 minutes, thus obtaining high-temperature resistant polyester filament.

[0103] The final high-temperature resistant polyester filament has a dual high-temperature resistant network structure constructed from polyimide powder and surface-modified diatomaceous earth. The tensile strength is 6.82 cN / dtex, the elongation at break is 23.85%, the dry heat shrinkage rate under the conditions of 180℃, 30 minutes and 0.01 cN / dtex pretension is 4.25%, the thermal decomposition temperature based on 5 wt% thermal weight loss is 441.9℃, the limiting oxygen index is 30.6%, the ultraviolet protection factor is 55.3, and the tensile strength retention rate after 300 hours of accelerated ultraviolet aging is 80.3%.

[0104] Comparative Example 1

[0105] A method for preparing polyester filament differs from Example 1 only in that: in the preparation process of surface-modified diatomaceous earth, diatomaceous earth powder is directly used for silane coupling agent modification treatment, and the diatomaceous earth powder is no longer calcined.

[0106] The final polyester filament has a breaking strength of 5.55 cN / dtex, a breaking elongation of 30.13%, a dry heat shrinkage rate of 7.44% under the conditions of 180℃, 30 minutes, and 0.01 cN / dtex pretension, a thermal decomposition temperature of 418.6℃ based on 5 wt% thermal weight loss, a limiting oxygen index of 29.7%, an ultraviolet protection factor of 42.1, and a breaking strength retention rate of 68.9% after 300 hours of accelerated ultraviolet aging.

[0107] Compared with Example 1, the limiting oxygen index of the polyester filament prepared in Comparative Example 1 showed no significant change. However, the breaking strength, thermal decomposition temperature (based on 5 wt% thermogravimetric analysis), UV protection factor, and breaking strength retention rate after 300 hours of accelerated UV aging decreased. The dry heat shrinkage and elongation at break increased under pre-tension conditions of 180°C, 30 minutes, and 0.01 cN / dtex. This is because the diatomaceous earth powder contains a certain amount of organic impurities, bound water, and debris that clogs the pores. If silane coupling agent modification is performed directly without calcination, the pores of the diatomaceous earth remain blocked by impurities, and the effective hydroxyl active sites on the outer surface and inner wall of the pores cannot be fully exposed, resulting in a significant decrease in the grafting amount and uniformity of the silane coupling agent. Insufficient silane coupling agent grafting directly weakens the chemical bond between the modified diatomaceous earth and the PET matrix, downgrading the interfacial bonding from strong chemical bonding to weak physical filling. The dispersion state of diatomaceous earth in the fiber is fundamentally deteriorated, and the "physical rigid skeleton" in the dual high-temperature resistant network structure cannot be effectively formed. Therefore, at high temperatures, the molecular chains of fibers are prone to slippage and deformation, leading to increased dry heat shrinkage and decreased thermal decomposition temperature. Simultaneously, mechanical properties (breaking strength) and aging durability (retention of breaking strength after 300 hours of accelerated UV aging) also significantly decrease due to poor interfacial bonding. Furthermore, diatomaceous earth agglomeration increases interfacial defects, correspondingly reducing the UV protection factor. Thus, calcination is a crucial step in ensuring the modification effect of diatomaceous earth and achieving a dual high-temperature resistant network structure.

[0108] Comparative Example 2

[0109] A method for preparing polyester filament differs from Example 1 only in that the silane coupling agent is replaced with a titanate coupling agent, manufactured by Tianchang Green Chemical Additives Factory, with the brand name TMC-201.

[0110] The final polyester filament had a breaking strength of 5.78 cN / dtex, a breaking elongation of 27.83%, a dry heat shrinkage rate of 5.71% under the conditions of 180℃, 30 minutes, and 0.01 cN / dtex pretension, a thermal decomposition temperature of 425.6℃ based on 5 wt% thermal weight loss, a limiting oxygen index of 29.2%, an ultraviolet protection factor of 45.2, and a breaking strength retention rate of 72.1% after 300 hours of accelerated ultraviolet aging.

[0111] Compared with Example 1, the limiting oxygen index of the polyester filament prepared in Comparative Example 2 did not change significantly. The breaking strength, thermal decomposition temperature based on 5wt% thermogravimetric analysis, UV protection factor, and breaking strength retention rate after 300 hours of UV accelerated aging decreased. However, the dry heat shrinkage and breaking elongation under the conditions of 180°C, 30 minutes, and 0.01cN / dtex pretension increased. This is because the KH-550 silane coupling agent used in Example 1 contains a primary amino group (-NH2) at its end. During high-temperature melt spinning, the primary amino group can undergo an amidation reaction with the ester group (-COO-) in the PET macromolecular chain to form a stable covalent chemical bond. At the same time, hydrogen bonding is also involved, which enables the modified diatomaceous earth to achieve strong chemical affinity and high interfacial bonding strength with the PET matrix. While the titanate coupling agent used in Comparative Example 2 can also undergo a condensation reaction with the hydroxyl groups on the diatomaceous earth surface to achieve grafting, its chemical structure lacks active functional groups capable of reacting chemically with PET ester groups. It can only provide physical compatibility and weak van der Waals forces for interfacial coupling, resulting in a chemical bond far weaker than the KH-550 system. Therefore, during high-temperature melt spinning, the interfacial bonding strength between the titanate coupling agent-modified diatomaceous earth and PET is significantly insufficient. The construction effect of the diatomaceous earth's "physical rigid skeleton" in the dual high-temperature resistant network structure is severely weakened, leading to a decreasing trend in tensile strength, thermal decomposition temperature, UV protection factor, and tensile strength retention rate after accelerated UV aging, while dry heat shrinkage and elongation at break show an increasing trend.

[0112] Comparative Example 3

[0113] A method for preparing polyester filament differs from Example 1 only in that polyimide powder is omitted.

[0114] The final polyester filament had a breaking strength of 5.22 cN / dtex, a breaking elongation of 32.34%, a dry heat shrinkage rate of 7.59% under the conditions of 180℃, 30 minutes, and 0.01 cN / dtex pretension, a thermal decomposition temperature of 405.7℃ based on 5 wt% thermal weight loss, a limiting oxygen index of 28.1%, an ultraviolet protection factor of 42.3, and a breaking strength retention rate of 65.9% after 300 hours of accelerated ultraviolet aging.

[0115] Compared with Example 1, the polyester filament prepared in Comparative Example 3 showed decreased limiting oxygen index, breaking strength, thermal decomposition temperature (based on 5 wt% thermogravimetric analysis), UV protection factor, and breaking strength retention rate after 300 hours of accelerated UV aging. However, it exhibited increased dry heat shrinkage and elongation at break under pre-tension conditions of 180°C, 30 minutes, and 0.01 cN / dtex. This is because the polyimide molecular chains in Example 1 contain a large number of aromatic heterocyclic conjugated rigid structures, which interweave with the PET molecular chains to form a rigid molecular network. This network effectively inhibits the slippage and thermo-oxidative degradation of PET molecular chains at high temperatures through steric hindrance and rigid constraints, while simultaneously increasing the thermal decomposition temperature of the PET matrix. Comparative Example 3, by omitting polyimide powder, only contains a single "physical rigid skeleton" constructed from modified diatomaceous earth, lacking the crucial component of the "rigid molecular network" provided by polyimide. Therefore, it cannot form the "physical + chemical" dual high-temperature resistant network structure described in this invention. The lack of rigid constraints from the molecular network makes PET molecular chains more susceptible to slippage, deformation, and thermo-oxidative degradation at high temperatures. This results in decreased tensile strength, thermal decomposition temperature, and retention of tensile strength after accelerated UV aging, while increasing dry heat shrinkage and elongation at break. The aromatic heterocyclic structure of the polyimide molecular chain inherently possesses UV absorption capabilities; the absence of polyimide also reduces the UV protection factor of polyester filaments. Furthermore, the entire system loses the intrinsic carbonization barrier function provided by polyimide, leading to a decrease in the limiting oxygen index.

[0116] Example 2

[0117] A method for preparing high-temperature resistant polyester filament differs from Example 1 only in that: after two-stage hot stretching and before relaxation heat setting, the surface of the stretched fiber is no longer subjected to plasma treatment.

[0118] The final high-temperature resistant polyester filament has a dual high-temperature resistant network structure constructed from polyimide powder and surface-modified diatomaceous earth. The tensile strength is 6.53 cN / dtex, the elongation at break is 27.38%, the dry heat shrinkage rate under the conditions of 180℃, 30 minutes and 0.01 cN / dtex pretension is 4.94%, the thermal decomposition temperature based on 5 wt% thermal weight loss is 435.3℃, the limiting oxygen index is 29.2%, the ultraviolet protection factor is 52.7, and the tensile strength retention rate after 300 hours of accelerated ultraviolet aging is 75.6%.

[0119] Compared with Example 1, the high-temperature resistant polyester filament prepared in Example 2 showed decreased breaking strength, thermal decomposition temperature (based on 5 wt% thermogravimetric analysis), limiting oxygen index, UV protection factor, and breaking strength retention rate after 300 hours of accelerated UV aging. However, the dry heat shrinkage and elongation at break under pretension conditions of 180°C, 30 minutes, and 0.01 cN / dtex increased. This is because Example 2 omitted plasma treatment, resulting in unactivated fiber surfaces, reduced number of surface polar groups, and weakened synergistic enhancement effect between the fiber and the internal dual high-temperature resistant network structure. This led to a decrease in interfacial bonding strength and surface anti-aging ability, specifically manifested as decreased breaking strength, thermal decomposition temperature, limiting oxygen index, and breaking strength retention rate after accelerated UV aging, while increased dry heat shrinkage and elongation at break. Simultaneously, the lack of micro-nano rough structures on the fiber surface also reduced its surface reflectivity to ultraviolet light, resulting in a corresponding decrease in the UV protection factor.

[0120] Example 3

[0121] A method for preparing high-temperature resistant polyester filament, the specific steps of which are as follows:

[0122] (1) Raw material preparation

[0123] Polyethylene terephthalate (PET) slices: The intrinsic viscosity of polyethylene terephthalate is 1.12 dL / g. This intrinsic viscosity was determined using the capillary viscometer method according to GB / T 14190-2017. The length, width, and height of the slices are 4 mm, 5 mm, and 2.5 mm, respectively.

[0124] Polyimide powder: average particle size 30μm, glass transition temperature ≥260℃ (determined by DSC method, referring to GB / T19466.2-2004), thermal decomposition temperature ≥500℃ based on 5wt% thermogravimetric analysis, density 1.3g / cm³, manufacturer: Shandong Kesim Special Materials Development Co., Ltd., grade: KSM-PI-30;

[0125] Diatomaceous earth powder: SiO2 mass fraction ≥85%, manufacturer is Linjiang City Dayuan Diatomaceous Earth New Material Ecological and Environmental Protection Technology Co., Ltd., grade is DZ300;

[0126] Silane coupling agent: KH-550, CAS No. 919-30-2, purity ≥98%;

[0127] Deionized water;

[0128] Anhydrous ethanol;

[0129] Compatibilizer: Maleic anhydride-grafted polyolefin elastomer, manufactured by Wuhan Jiyesheng Chemical Co., Ltd., brand name A00856;

[0130] Antioxidant: Antioxidant 168, manufactured by BASF, brand name Irgafos 168;

[0131] Lubricant: Ethylene bis-stearamide, manufactured by Crodamide International Limited, UK, brand name Crodamide EBS;

[0132] Flame retardant: Nano-sized magnesium hydroxide with an average particle size of 50nm, manufactured by Liaoning Jinghua New Material Co., Ltd., brand name JH-MH-50;

[0133] Ultraviolet absorber: UV-531, CAS No. 1843-05-6, purity ≥99.0%;

[0134] (2) Preparation of surface-modified diatomaceous earth

[0135] (2.1) Calcination treatment: The diatomaceous earth powder was heated to 550°C at a heating rate of 4°C / min and calcined for 3 hours;

[0136] (2.2) Modification treatment: The calcined diatomaceous earth powder, silane coupling agent, ethanol and water were mixed and reacted at 75°C for 2.5 hours. The mass of the silane coupling agent accounted for 4% of the mass of the calcined diatomaceous earth powder, and the mass ratio of silane coupling agent, ethanol and water was 1:6:3.

[0137] (2.3) Post-processing: The material modified by silane coupling agent is sequentially filtered, washed, dried, crushed and sieved to obtain surface-modified diatomaceous earth.

[0138] The washing process involves first washing with deionized water three times, and then washing with anhydrous ethanol three times.

[0139] Drying involves drying the washed filter cake under a vacuum of -0.09 MPa and a temperature of 110°C for 5 hours.

[0140] The grinding and sieving process involves passing the material through a 450-mesh sieve.

[0141] (3) Melt blending

[0142] (3.1) Polyethylene terephthalate chips are premixed with compatibilizer, antioxidant and lubricant to obtain a premix;

[0143] (3.2) The premix was melt-blended with surface-modified diatomaceous earth, polyimide powder, flame retardant and ultraviolet absorber to obtain composite masterbatch;

[0144] By weight, the following components are present: 60 parts polyethylene terephthalate chips, 8 parts surface-modified diatomaceous earth, 10 parts polyimide powder, 6 parts compatibilizer, 3 parts antioxidant, 2 parts lubricant, 15 parts flame retardant, and 4.5 parts ultraviolet absorber.

[0145] Melt blending was carried out using a twin-screw extruder. The process parameters for melt blending were: zone 1 temperature 245℃, zone 2 temperature 260℃, zone 3 temperature 270℃, zone 4 temperature 275℃, die head temperature 272℃, screw speed 250 rpm, and melt residence time 3 minutes.

[0146] (4) Melt spinning

[0147] (4.1) The composite masterbatch is dried at 125°C for 4 hours to reduce the moisture content of the composite masterbatch to below 0.02wt%, and then melted at 290°C. The masterbatch is then extruded through a spinneret to form nascent fibers. The spinneret has circular spinneret holes with an outlet diameter of 0.3mm.

[0148] (4.2) After the nascent fiber is cooled and solidified, it is subjected to two-stage hot stretching to obtain stretched fiber. The first stage of stretching is carried out in a hot water bath at a water temperature of 85℃ and a stretching ratio of 1.8. The second stage of stretching is carried out on a hot roller at a roller surface temperature of 140℃ and a stretching ratio of 3.0.

[0149] (4.3) Plasma treatment of the surface of the drawn fibers

[0150] The plasma treatment power is 270W, and the plasma treatment time is 1.0 second;

[0151] The working medium for plasma treatment is a mixture of argon and oxygen, with argon comprising 85% of the volume in the mixture.

[0152] (4.4) The plasma-treated drawn fiber is subjected to relaxation heat setting at 190°C. The running time of the drawn fiber in the relaxation heat setting zone is 2 minutes, thus obtaining high-temperature resistant polyester filament.

[0153] The final high-temperature resistant polyester filament has a dual high-temperature resistant network structure constructed from polyimide powder and surface-modified diatomaceous earth. The tensile strength is 7.14 cN / dtex, the elongation at break is 20.02%, the dry heat shrinkage rate under the conditions of 180℃, 30 minutes and 0.01 cN / dtex pretension is 3.44%, the thermal decomposition temperature based on 5 wt% thermal weight loss is 452.6℃, the limiting oxygen index is 32.1%, the ultraviolet protection factor is 62.1, and the tensile strength retention rate after 300 hours of accelerated ultraviolet aging is 84.7%.

[0154] Example 4

[0155] A method for preparing high-temperature resistant polyester filament, the specific steps of which are as follows:

[0156] (1) Raw material preparation

[0157] Polyethylene terephthalate (PET) slices: The intrinsic viscosity of polyethylene terephthalate is 1.12 dL / g. This intrinsic viscosity was determined using the capillary viscometer method according to GB / T 14190-2017. The length, width, and height of the slices are 4 mm, 5 mm, and 2.5 mm, respectively.

[0158] Polyimide powder: average particle size 40μm, glass transition temperature ≥260℃ (determined by DSC method, referring to GB / T19466.2-2004), thermal decomposition temperature ≥500℃ based on 5wt% thermogravimetric analysis, density 1.3g / cm³, manufacturer: Shandong Kesim Special Materials Development Co., Ltd., grade: KSM-PI-40;

[0159] Diatomaceous earth powder: SiO2 mass fraction ≥85%, manufacturer is Shengzhou Huali Diatomaceous Earth Products Co., Ltd., grade is CD05;

[0160] Silane coupling agent: KH-570, CAS No. 2530-85-0, purity ≥98.0%;

[0161] Deionized water;

[0162] Anhydrous ethanol;

[0163] Compatibilizer: Maleic anhydride-grafted polyethylene, manufactured by Arkema, France, brand name OREVAC18300;

[0164] Antioxidant: Antioxidant 1010, manufactured by BASF, brand name Irganox 1010;

[0165] Lubricant: Ethylene bis-stearamide, manufactured by CMS Chemical Industries, Indonesia, brand name HI-LUBP-200;

[0166] Flame retardant: Nano-sized magnesium hydroxide with an average particle size of 40nm, manufactured by Zhejiang Zhitai Nano Micro New Materials Co., Ltd., brand name ZT-MH01;

[0167] Ultraviolet absorber: UV-326, CAS number 3896-11-5, purity ≥99.0%;

[0168] (2) Preparation of surface-modified diatomaceous earth

[0169] (2.1) Calcination treatment: The diatomaceous earth powder was heated to 600℃ at a heating rate of 5℃ / min and calcined for 4 hours;

[0170] (2.2) Modification treatment: The calcined diatomaceous earth powder, silane coupling agent, ethanol and water are mixed and reacted at 80°C for 3 hours. The mass of silane coupling agent accounts for 5% of the mass of calcined diatomaceous earth powder, and the mass ratio of silane coupling agent, ethanol and water is 1:6:3.

[0171] (2.3) Post-processing: The material modified by silane coupling agent is sequentially filtered, washed, dried, crushed and sieved to obtain surface-modified diatomaceous earth.

[0172] The washing process involves first washing twice with deionized water, and then washing twice with anhydrous ethanol.

[0173] Drying involves drying the washed filter cake under a vacuum of -0.085 MPa and a temperature of 120°C for 6 hours.

[0174] The grinding and sieving process involves passing the material through a 500-mesh sieve.

[0175] (3) Melt blending

[0176] (3.1) Polyethylene terephthalate chips are premixed with compatibilizer, antioxidant and lubricant to obtain a premix;

[0177] (3.2) The premix was melt-blended with surface-modified diatomaceous earth, polyimide powder, flame retardant and ultraviolet absorber to obtain composite masterbatch;

[0178] By weight, the following components are present: 70 parts polyethylene terephthalate chips, 5 parts surface-modified diatomaceous earth, 8 parts polyimide powder, 4 parts compatibilizer, 2 parts antioxidant, 1 part lubricant, 10 parts flame retardant, and 3 parts ultraviolet absorber.

[0179] Melt blending was carried out using a twin-screw extruder. The process parameters for melt blending were: zone 1 temperature 250℃, zone 2 temperature 265℃, zone 3 temperature 275℃, zone 4 temperature 280℃, die head temperature 275℃, screw speed 300 rpm, and melt residence time 2 minutes.

[0180] (4) Melt spinning

[0181] (4.1) The composite masterbatch is dried at 130°C for 3 hours to reduce the moisture content of the composite masterbatch to below 0.02wt%, and then melted at 295°C. The masterbatch is extruded through a spinneret to form nascent fibers. The spinneret has circular spinneret holes with an outlet diameter of 0.3mm.

[0182] (4.2) After the nascent fiber is cooled and solidified, it is subjected to two-stage hot stretching to obtain stretched fiber. The first stage of stretching is carried out in a hot water bath at a water temperature of 90℃ and a stretching ratio of 2.0. The second stage of stretching is carried out on a hot roller at a roller surface temperature of 150℃ and a stretching ratio of 3.1.

[0183] (4.3) Plasma treatment of the surface of the drawn fibers

[0184] The plasma treatment power is 400W, and the plasma treatment time is 0.5 seconds;

[0185] The working medium for plasma treatment is a mixture of argon and oxygen, with argon comprising 90% of the volume in the mixture.

[0186] (4.4) The plasma-treated drawn fiber is subjected to relaxation heat setting at 200°C. The running time of the drawn fiber in the relaxation heat setting zone is 1 minute, thus obtaining high-temperature resistant polyester filament.

[0187] The final high-temperature resistant polyester filament has a dual high-temperature resistant network structure constructed from polyimide powder and surface-modified diatomaceous earth. The tensile strength is 8.13 cN / dtex, the elongation at break is 15.41%, the dry heat shrinkage rate under the conditions of 180℃, 30 minutes and 0.01 cN / dtex pretension is 2.24%, the thermal decomposition temperature based on 5 wt% thermal weight loss is 457.3℃, the limiting oxygen index is 34.8%, the ultraviolet protection factor is 67.9, and the tensile strength retention rate after 300 hours of accelerated ultraviolet aging is 92.6%.

[0188] Example 5

[0189] A method for preparing high-temperature resistant polyester filament, the specific steps of which are as follows:

[0190] (1) Raw material preparation

[0191] Polyethylene terephthalate (PET) slices: The intrinsic viscosity of PET is 1.12 dL / g, which was determined by capillary viscometer method according to GB / T 14190-2017; the length, width, and height of the slices are 4 mm, 5 mm, and 2.5 mm, respectively.

[0192] Polyimide powder: average particle size 30μm, glass transition temperature ≥260℃ (determined by DSC method, referring to GB / T19466.2-2004), thermal decomposition temperature ≥500℃ based on 5wt% thermogravimetric analysis, density 1.3g / cm³, manufacturer: Shandong Kesim Special Materials Development Co., Ltd., grade: KSM-PI-30;

[0193] Diatomaceous earth powder: SiO2 mass fraction ≥85%, manufacturer is Linjiang City Dayuan Diatomaceous Earth New Material Ecological and Environmental Protection Technology Co., Ltd., grade is DZ300;

[0194] Silane coupling agent: KH-560, CAS number 2530-83-8, purity ≥98.0%;

[0195] Deionized water;

[0196] Anhydrous ethanol;

[0197] Compatibilizer: Maleic anhydride-grafted polyolefin elastomer, manufactured by Wuhan Jiyesheng Chemical Co., Ltd., brand name A00856;

[0198] Antioxidant: Antioxidant 1076, manufactured by BASF, brand name Irganox 1076;

[0199] Lubricant: Ethylene bis-stearamide, manufactured by Crodamide International Limited, UK, brand name Crodamide EBS;

[0200] Flame retardant: Nano-sized magnesium hydroxide with an average particle size of 50nm, manufactured by Liaoning Jinghua New Material Co., Ltd., brand name JH-MH-50;

[0201] Ultraviolet absorber: UV-329, CAS No. 3147-75-9, purity ≥99.0%;

[0202] (2) Preparation of surface-modified diatomaceous earth

[0203] (2.1) Calcination treatment: The diatomaceous earth powder was heated to 500℃ at a heating rate of 3℃ / min and calcined for 2 hours;

[0204] (2.2) Modification treatment: The calcined diatomaceous earth powder, silane coupling agent, ethanol and water are mixed and reacted at 70°C for 2 hours. The mass of the silane coupling agent accounts for 3% of the mass of the calcined diatomaceous earth powder, and the mass ratio of silane coupling agent, ethanol and water is 1:6:3.

[0205] (2.3) Post-processing: The material modified by silane coupling agent is sequentially filtered, washed, dried, crushed and sieved to obtain surface-modified diatomaceous earth.

[0206] The washing process involves first washing with deionized water three times, and then washing with anhydrous ethanol three times.

[0207] Drying involves drying the washed filter cake under a vacuum of -0.09 MPa and a temperature of 100°C for 4 hours.

[0208] The grinding and sieving process involves passing the material through a 400-mesh sieve.

[0209] (3) Melt blending

[0210] (3.1) Polyethylene terephthalate chips are premixed with compatibilizer, antioxidant and lubricant to obtain a premix;

[0211] (3.2) The premix was melt-blended with surface-modified diatomaceous earth, polyimide powder, flame retardant and ultraviolet absorber to obtain composite masterbatch;

[0212] By weight, the following components are present: 55 parts polyethylene terephthalate chips, 7.5 parts surface-modified diatomaceous earth, 11 parts polyimide powder, 7 parts compatibilizer, 3 parts antioxidant, 2 parts lubricant, 18 parts flame retardant, and 5 parts ultraviolet absorber.

[0213] Melt blending was carried out using a twin-screw extruder. The process parameters for melt blending were: zone 1 temperature 240℃, zone 2 temperature 255℃, zone 3 temperature 265℃, zone 4 temperature 270℃, die head temperature 270℃, screw speed 200 rpm, and melt residence time 3.5 minutes.

[0214] (4) Melt spinning

[0215] (4.1) The composite masterbatch is dried at 120°C for 4.5 hours to reduce the moisture content of the composite masterbatch to below 0.02wt%, and then melted at 285°C. The masterbatch is then extruded through a spinneret to form nascent fibers. The spinneret has circular spinneret holes with an outlet diameter of 0.3mm.

[0216] (4.2) After the nascent fiber is cooled and solidified, it is subjected to two-stage hot stretching to obtain stretched fiber. The first stage of stretching is carried out in a hot water bath at a water temperature of 80℃ and a stretching ratio of 1.6. The second stage of stretching is carried out on a hot roller at a roller surface temperature of 130℃ and a stretching ratio of 2.8.

[0217] (4.3) Plasma treatment of the surface of the drawn fibers

[0218] The plasma treatment power is 300W, and the plasma treatment time is 1.5 seconds;

[0219] The working medium for plasma treatment is a mixture of argon and oxygen, with argon comprising 80% of the volume in the mixture.

[0220] (4.4) The plasma-treated drawn fiber is subjected to relaxation heat setting at 180°C. The running time of the drawn fiber in the relaxation heat setting zone is 2.5 minutes, thus obtaining high-temperature resistant polyester filament.

[0221] The final high-temperature resistant polyester filament has a dual high-temperature resistant network structure constructed from polyimide powder and surface-modified diatomaceous earth. The tensile strength is 7.07 cN / dtex, the elongation at break is 22.18%, the dry heat shrinkage rate under the conditions of 180℃, 30 minutes and 0.01 cN / dtex pretension is 3.06%, the thermal decomposition temperature based on 5 wt% thermal weight loss is 444.8℃, the limiting oxygen index is 31.5%, the ultraviolet protection factor is 54.9, and the tensile strength retention rate after 300 hours of accelerated ultraviolet aging is 83.5%.

[0222] Based on the combined results of Examples 1-5 and Comparative Examples 1-3, it can be seen that the overall performance of polyester filament exhibits a clear gradient of "Examples 1, 3-5 > Example 2 > Comparative Examples 1-3". Among them, Comparative Examples 1-3 had the worst overall performance because they lacked calcination treatment, used titanate coupling agents, or omitted polyimide, resulting in incomplete core components and the inability to effectively construct the dual high-temperature resistant network structure. Although plasma treatment was omitted in Example 2, the dual high-temperature resistant network structure constructed by the synergistic effect of calcination treatment, silane coupling agent, and polyimide powder was still complete. This resulted in significantly better dry heat shrinkage rate (at 180°C, 30 minutes, and 0.01 cN / dtex pretension), thermal decomposition temperature (based on 5 wt% thermal weight loss), and breaking strength of the polyester filament compared to Comparative Examples 1-3. Moreover, the dry heat shrinkage rate and thermal decomposition temperature were also significantly better than those of ordinary polyester filament. Examples 1, 3-5, on the basis of complete core components, further introduced plasma treatment to enhance the synergistic effect between the surface and internal dual high-temperature resistant network structure through fiber surface activation, thereby achieving optimal overall performance. This indicates that even without plasma treatment, the synergistic effect of the core components can already construct an effective dual high-temperature resistant network structure; while plasma treatment can further enhance the internal and external synergistic effect between the fiber surface and the internal dual high-temperature resistant network structure through surface activation, effectively improving the thermal stability and mechanical properties of the fiber.

Claims

1. A method for preparing high-temperature resistant polyester filament, characterized in that, The raw materials, including polyethylene terephthalate chips, polyimide powder and surface-modified diatomaceous earth, are melt-blended to obtain a composite masterbatch. The composite masterbatch is then melt-spun to obtain high-temperature resistant polyester filament. The preparation process of surface-modified diatomaceous earth includes: first, calcining the diatomaceous earth powder, and then modifying it with a silane coupling agent; The silane coupling agent is selected from one of KH-550, KH-560, and KH-570.

2. The method for preparing a high-temperature resistant polyester filament according to claim 1, characterized in that, The calcination process is as follows: the diatomaceous earth powder is heated to 500-600℃ at a heating rate of 3-5℃ / min and calcined for 2-4 hours.

3. The method for preparing a high-temperature resistant polyester filament according to claim 1, characterized in that, The process of silane coupling agent modification is as follows: calcined diatomaceous earth powder, silane coupling agent, ethanol and water are mixed and reacted at 70~80℃ for 2~3 hours. The mass of silane coupling agent accounts for 3%~5% of the mass of calcined diatomaceous earth powder.

4. The method for preparing a high-temperature resistant polyester filament according to claim 1, characterized in that, The preparation process of surface-modified diatomaceous earth also includes post-treatment after silane coupling agent modification; The post-processing involves sequentially filtering, washing, drying, pulverizing, and sieving the material after modification with the silane coupling agent.

5. The method for preparing a high-temperature resistant polyester filament according to claim 1, characterized in that, By weight, the polyethylene terephthalate chips are 50-70 parts, the surface-modified diatomaceous earth is 5-10 parts, and the polyimide powder is 8-12 parts.

6. The method for preparing a high-temperature resistant polyester filament according to claim 5, characterized in that, The raw materials also include compatibilizers, antioxidants and lubricants; by weight, the compatibilizer is 4-8 parts, the antioxidant is 2-4 parts, and the lubricant is 1-3 parts. Polyethylene terephthalate chips were premixed with compatibilizer, antioxidant and lubricant to obtain a premix; then the premix was melt-blended with surface-modified diatomaceous earth and polyimide powder.

7. The method for preparing a high-temperature resistant polyester filament according to claim 6, characterized in that, The raw materials also include flame retardants and ultraviolet absorbers; by weight, the flame retardant is 10-20 parts and the ultraviolet absorber is 3-6 parts. The premix is ​​melt-blended with surface-modified diatomaceous earth, polyimide powder, flame retardant and ultraviolet absorber.

8. The method for preparing a high-temperature resistant polyester filament according to claim 1, characterized in that, Melt spinning includes the following steps: The composite masterbatch is dried at 120~130℃, melted at 285~295℃, and extruded through a spinneret to form nascent fibers. After the nascent fibers are cooled and solidified, they are subjected to two stages of hot stretching to obtain stretched fibers. The first stage of stretching is carried out in a hot water bath at a temperature of 80~90℃ and a stretching ratio of 1.5~2.

0. The second stage of stretching is carried out on a hot roller at a surface temperature of 130~150℃ and a stretching ratio of 2.5~3.

1. The drawn fibers are subjected to relaxation heat setting at 180~200℃, and the running time of the drawn fibers in the relaxation heat setting zone is 1~3 minutes.

9. The method for preparing a high-temperature resistant polyester filament according to claim 8, characterized in that, Between the two-stage thermal stretching and relaxation heat setting, plasma treatment of the surface of the stretched fibers is also included; The plasma treatment power is 200~400W, and the plasma treatment time is 0.5~2.0 seconds; The working medium for plasma treatment is a mixture of argon and oxygen, with argon accounting for 80% to 90% of the volume of the mixture.

10. A high-temperature resistant polyester filament, characterized in that, It is prepared by the method for preparing a high-temperature resistant polyester filament according to any one of claims 1 to 9; The high-temperature resistant polyester filament has a breaking strength of 6.82~8.13 cN / dtex, a breaking elongation of 15.41%~23.85%, a dry heat shrinkage rate of 2.24%~4.25% under the conditions of 180℃, 30 minutes, and 0.01 cN / dtex pretension, a thermal decomposition temperature of 441.9~457.3℃ based on 5wt% thermogravimetric analysis, a limiting oxygen index of 30.6%~34.8%, an ultraviolet protection factor of 54.9~67.9, and a breaking strength retention rate of 80.3%~92.6% after 300 hours of accelerated ultraviolet aging.