Polyester fiber suitable for non-aqueous medium dyeing and a method for preparing the same

Abstract

The application belongs to the technical field of synthetic fiber modification, and discloses polyester fiber suitable for non-aqueous medium dyeing and a preparation method thereof. First, terephthalic acid and ethylene glycol are used as raw materials, a composite bimetallic catalyst and an esterification promoter containing a siloxane group are added, and beating is performed to form slurry. Then, the slurry is continuously fed into an esterification reactor for esterification reaction, and the esterification product is subjected to polycondensation reaction to obtain polyester melt. Finally, the polyester melt is sequentially subjected to casting, granulation and solid-phase tackification to obtain high-viscosity polyester chips, and then melt spinning is performed to obtain polyester fiber suitable for non-aqueous medium dyeing. From the start of feeding the esterification product, the esterification reactor always contains 40-60% of the esterification product based on the effective volume. The oligomer content in the product is less than 0.6wt%, and the proportion of cyclic trimers in the oligomers is more than 60%. The method effectively solves the problems of color spots and uneven dyeing caused by the precipitation of oligomers, and the product has excellent dyeing performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polyester synthesis, and relates to a polyester fiber suitable for non-aqueous medium dyeing and a preparation method thereof. BACKGROUND

[0002] As the largest synthetic fiber in the world, polyester fiber is widely used due to its excellent mechanical properties and cost advantage. However, the traditional water medium dyeing process has the problems of high water consumption and high pollution. About 100-200 tons of water are needed for every ton of textile produced, and a large amount of difficult-to-treat wastewater containing dyes and auxiliaries is generated. To solve this problem, non-aqueous medium dyeing technologies such as silicone solvent dyeing and supercritical carbon dioxide fluid dyeing are considered as potential green alternatives. However, when traditional polyester fibers are directly applied to these technologies, there are two inherent problems: first, the oligomers (about 1.5%-3.0% of the weight of the chip) produced during the polymerization process, especially the chemically stable cyclic trimers, have very low solubility in hydrophobic non-aqueous media, and are easily migrated to the surface of the fiber and crystallized, causing serious color spots, uneven dyeing, and blocking of equipment pipes. Moreover, 70%-80% of the oligomers are produced during the esterification stage; second, the polyester macromolecular chain lacks affinity with the medium such as silicone, resulting in low dyeing rate of the dye, which requires more stringent dyeing conditions.

[0003] To overcome these difficulties, existing technologies focus on improving the post-treatment stage of dyeing, mainly divided into two categories. One is to develop oligomer removers or dyeing auxiliaries, such as the patent CN104562776A which uses a complex auxiliary to inhibit the adsorption of oligomers on the surface of the fiber. The other focuses on developing a new water-free dyeing process, such as the patent CN117286728A which uses supercritical carbon dioxide as the dyeing medium, completely avoiding the use of water; and the patent CN201410152912A which uses an organic solvent system such as alkane and silicone oil.

[0004] CN104594072A uses a small amount of active dye solvent and carbon dioxide as the dyeing medium to reduce the toxicity of the medium and realize solvent recycling. Although this patent involves non-aqueous medium dyeing, its technical focus is on the replacement of the medium and the recovery of the solvent in the dyeing link, and it does not involve the improvement or process optimization of the esterification reactor in the polyester synthesis process.

[0005] In addition, when the existing technology introduces a third component (such as CN202311690077) to give the fiber functionality or improve dyeability, it is often difficult to balance its core mechanical properties; or through surface modification treatment (such as CN101922121A), it cannot guarantee the durability of the dyeing effect, and cannot realize the permanent and intrinsic modification of the fiber itself.

[0006] In summary, the existing polyester fiber has a high oligomer content, which can cause color spots during dyeing and rinsing. The existing technology mainly uses post-treatment or changes the medium to inhibit the precipitation of oligomers, but it cannot reduce the total amount of oligomers. Oligomers still exist in the fiber, which can cause color spots in subsequent processing or use. In addition, improving the dyeing affinity requires sacrificing fiber performance or high cost, which cannot be considered together. The specific problems are as follows:

[0007] (1) The existing technology mainly uses post-treatment or adds additives to inhibit the precipitation of oligomers. This method can only prevent the adhesion of oligomers to the fiber surface after they have been generated, and cannot reduce the total amount of oligomers. Oligomers still exist in the fiber, which can cause color spots in subsequent processing or use. In addition, improving the dyeing affinity requires sacrificing fiber performance or high cost, which cannot be considered together. The specific problems are as follows:

[0008] (2) The current esterification process is mainly intermittent or semi-intermittent, which has a significant "reaction plateau". In this stage, the reaction system is heterogeneous, the rate is slow, the energy consumption is high, and the side reactions increase, which directly leads to a wide molecular weight distribution (PDI>2.5) and high oligomer content, which poses a quality risk for subsequent dyeing;

[0009] (3) The addition of a third monomer to introduce a medium group often destroys the regularity of the polyester molecule, sacrificing its excellent mechanical strength, dimensional stability, and thermal stability. Surface treatment / coating: the medium coating treatment of the fiber is temporary and can easily fall off or wear out during subsequent friction, washing, or processing, which cannot guarantee the durability of the dyeing effect. These methods cannot achieve permanent and intrinsic fiber modification;

[0010] (4) Other organic solvent dyeing: may have new problems such as solvent toxicity, difficulty in recycling, residual odor, and poor dye solubility, which replace water pollution problems with other environmental or cost problems.

[0011] Therefore, it is of great significance to study a polyester fiber suitable for non-aqueous medium dyeing and its preparation method to solve the problems in the existing technology. SUMMARY

[0012] The purpose of the present application is to solve the problems in the prior art and provide a polyester fiber suitable for non-aqueous medium dyeing and its preparation method.

[0013] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0014] The application discloses a preparation method of polyester fibers suitable for non-aqueous medium dyeing, which comprises the following steps: first, taking terephthalic acid (PTA) and ethylene glycol (EG) as raw materials, adding a composite bimetallic catalyst and an esterification promoter containing a siloxane group, and beating to form a slurry; then, continuously feeding the slurry into an esterification reactor for esterification reaction; when the esterification product accounts for 40-60% of the effective volume of the esterification reactor, continuously feeding the slurry into the esterification reactor while sequentially feeding the esterification product into a pre-polycondensation reactor and a final polycondensation reactor for polycondensation reaction to obtain a polyester melt; finally, sequentially passing the polyester melt through a casting belt, a granulating device and a solid-phase tackifying device to obtain high-viscosity polyester chips, drying the polyester chips, and melt spinning to obtain the polyester fibers suitable for non-aqueous medium dyeing.

[0015] The composite bimetallic catalyst is a titanium-zinc bimetallic catalyst or a titanium-magnesium bimetallic catalyst; a single titanium catalyst is prone to hydrolysis, and the product is yellow; the bimetallic catalyst can improve the electronegativity, maintain good hydrolysis resistance and dispersion in the melt; through the strong coordination ability of the titanium metal center in the bimetallic catalyst, the carboxyl of PTA and the terminal hydroxyl of the siloxane-containing esterification promoter are chelated to form a high-efficiency reaction transition state, greatly reducing the esterification reaction energy barrier, significantly shortening the esterification reaction time, inhibiting side reactions from the source, reducing the generation of oligomers and narrowing the molecular weight distribution;

[0016] The esterification promoter containing a siloxane group is hydroxyl-terminated polydimethylsiloxane I or carboxyl-terminated polydimethylsiloxane; the number average molecular weight of the esterification promoter containing a siloxane group is 400-2000 g / mol; the hydroxyl-terminated polydimethylsiloxane I or carboxyl-terminated polydimethylsiloxane has a soft linear long chain, which can minimize the interference with the properties of the polyester body while ensuring flexibility and compatibility;

[0017] When the number average molecular weight of the siloxane group-containing esterization promoter is too low, the siloxane segment is too short to effectively play the modification function of similar phase solubility and may interfere with the system. One of the cores of the present application is to impart inherent affinity of the fiber to the dyeing medium through the connected siloxane segment. The siloxane with a number average molecular weight lower than 400 g / mol has a segment that is too short to form a large enough hydrophobic and flexible region. Even if it is successfully connected, its effect on dyeing promotion is minimal, and it cannot achieve a high dyeing rate of more than 90%, making the modification meaningless. At the same time, siloxane with too low a number average molecular weight is closer to small molecules, and its volatility increases during the condensation process at high temperature and high vacuum, which may lead to loss of effective ingredients and may condense in the equipment pipeline, causing blockage or contamination. If the molecular weight is too high, the reactivity is reduced and the steric hindrance is increased, which seriously damages the performance of the polyester body. The present application requires that the siloxane promoter must be able to move quickly and form a high-efficiency chelation reaction center with the double metal catalyst and the PTA carboxyl group. When the number average molecular weight exceeds 2000 g / mol, the siloxane molecular chain is too long and bulky, and its movement and diffusion ability in the viscous polymer melt is poor, making it difficult to contact the catalyst and reactant in time and effectively, resulting in a significant decrease in catalytic promotion efficiency. The long siloxane segment is connected to the rigid polyester backbone as a flexible chain, which produces a huge steric hindrance effect, seriously hindering the close arrangement and crystallization of the polyester molecular chain, resulting in a sharp decrease in the strength, modulus and hardness of the fiber, a significant decrease in the melting point and glass transition temperature, poor heat resistance of the fiber, abnormal melt strength, high breakage rate during spinning process, and poor compatibility: the long siloxane chain has a greater difference in chemical structure with the polyester body, which may cause phase separation during polymerization or melting, forming micro-uniform regions and becoming defect points of the material.

[0018] The intrinsic viscosity of the high-viscosity polyester chip is 0.70-0.85 dL / g; the solid-phase viscosity increase to 0.70-0.85 dL / g is to ensure that the fiber has sufficient molecular weight and melt strength to support subsequent stable spinning and obtain excellent mechanical properties, so as to meet the requirements of specific dyeing process and final use scenario;

[0019] From the start of the esterification product, there is always 40-60% of the esterification product in the effective volume of the esterification reactor.

[0020] As a preferred technical solution:

[0021] The preparation method of polyester fiber for non-aqueous medium dyeing as described above, the molar ratio of terephthalic acid and ethylene glycol is 1:1.08~1.20, the addition amount of the composite bimetallic catalyst is 50~180 ppm of the mass of terephthalic acid (in batching, the effective component of the added composite bimetallic catalyst, that is, the total mass of pure metal atoms, should account for 50 to 1,100 ppm of the mass of PTA raw material); the addition amount of the siloxane group-containing esterification promoter is 1.0~4.0% of the mass of terephthalic acid, which is less than 1.0%, the catalytic promotion effect is insufficient, and the dyeing modification is invalid. The reasons are as follows: ① The siloxane concentration is too low, which means that the number of molecules capable of forming a transition state with titanium metal centers in the reaction system is insufficient, which will significantly weaken the catalytic synergistic effect, and cannot effectively reduce the esterification activation energy, which will greatly reduce the effect of shortening the esterification platform period and inhibiting the generation of oligomers. The reaction may still be trapped in the traditional "platform period", and the oligomer content cannot be effectively reduced to below 0.7%. ② The total amount of siloxane segments connected to the polyester macromolecular chain is too small, and there is a lack of enough siloxane segments in the fiber during subsequent dyeing to produce a strong "similar phase solubility" effect with the dye bath medium; as a result, the dyeing affinity is not significantly improved, and the dye uptake rate cannot break through 90%, and the advantage is lost compared with traditional polyester fibers. When it is higher than 4.0%, ① Excessive siloxane segments are connected to the polyester main chain, which will seriously damage the regularity and crystallization ability of the polyester molecular chain. The mechanical properties decrease significantly: the strength and modulus of the fiber decrease sharply, and the fiber becomes soft but weak, which cannot meet the requirements of wear or industrial use. The thermal performance deteriorates: the glass transition temperature and melting point decrease, and the heat resistance of the fiber becomes poor. The spinnability deteriorates: the melt strength may be insufficient, and the fiber is prone to breakage during spinning drafting, resulting in low yield. ② Excessive siloxane may change the physical and chemical properties of the reaction system (such as viscosity), which may interfere with the normal esterification and polycondensation process. They may form local enrichment zones in the system and undergo self-condensation and other side reactions, not only wasting raw materials, but also possibly becoming new oligomers or impurities, affecting product purity; from an economic point of view, the cost of the siloxane promoter is relatively high, and excessive addition will unnecessarily increase the cost of raw materials.

[0022] The preparation method of polyester fiber for non-aqueous medium dyeing as described above, the composite bimetallic catalyst is a complex of tetrabutyl titanate, dihydric alcohol, hydroxyl-terminated polydimethylsiloxane II and metal salt.

[0023] The dihydric alcohol is an aliphatic dihydric alcohol with a carbon atom number of 2-5, and the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane II is 300-800 g / mol; if the number average molecular weight is too high, the siloxane segment is too long to react, which easily causes the agglomeration of the catalyst particles, the catalyst particles are too large to be dissolved in the dihydric alcohol, and if the content is too low, the hydrolysis resistance cannot meet the use requirements; if the number average molecular weight is too low, the high reactivity and water repellency of the siloxane are reduced; the metal salt is zinc acetate or magnesium acetate;

[0024] The molar ratio of tetrabutyl titanate, dihydric alcohol, hydroxyl-terminated polydimethylsiloxane II and metal salt is 1:2.75-3:0.25-0.5:1-1.25.

[0025] The liquid level in the esterification reactor is kept constant by controlling the feed amount and discharge amount.

[0026] The esterification conditions are as follows: temperature 245-260°C, pressure 0.05-0.35 MPa, and esterification rate not less than 97%.

[0027] The polycondensation reaction conditions are as follows: pre-polycondensation temperature 265-275°C, pressure 2-8 kPa; and final polycondensation temperature 265-275°C, vacuum degree less than or equal to 80 Pa.

[0028] The intrinsic viscosity of the polyester melt is 0.60-0.70 dL / g.

[0029] The solid-phase viscosity-increasing conditions are as follows: under the protection of nitrogen, the treatment is carried out at 200-220°C for 8-15 hours.

[0030] The melt spinning process parameters are as follows: spinning temperature 285-295°C, draw ratio 3.5-4.5 times, and heat setting temperature 160-180°C.

[0031] The application also provides the polyester fiber for non-aqueous medium dyeing prepared by the method.

[0032] The polyester fiber for non-aqueous medium dyeing has a molecular weight distribution index (PDI) less than 2.2, and the macromolecular chain is bonded with a siloxane segment.

[0033] As a preferred technical solution:

[0034] The polyester fiber suitable for non-aqueous medium dyeing is immersed in the dye solution, and dyed at 110-130 DEG C for 30-60 minutes.

[0035] The silicone medium is decamethylcyclopentasiloxane (D5) or octamethylcyclotetrasiloxane (D4).

[0036] The polyester fiber suitable for non-aqueous medium dyeing has an up-take rate of the disperse dye of not less than 90%, and a dyeing uniformity of 4-5 grades without color spot phenomenon.

[0037] Invention principle:

[0038] Traditional polyester synthesis generally uses a single antimony-based catalyst (such as ethylene glycol antimony), which has limited catalytic efficiency and insufficient selectivity inhibition ability for side reactions. In the high-temperature esterification process, it cannot effectively guide the reaction path, resulting in a large number of side reactions, generating oligomers equivalent to 1.5-3.0% of the mass of esterification products, of which cyclic trimers account for more than 60%. These oligomers are the source of color spots and white powder in subsequent processing.

[0039] The present application utilizes the chelation of the catalyst with the esterification promoter and the raw material, effectively reducing the generation of oligomers in the esterification reaction process, and solving the problem of easy precipitation of oligomers to form color spots during polyester fiber dyeing from the source. Specifically:

[0040] The present application uses titanium-zinc bimetallic catalyst or titanium-magnesium bimetallic catalyst, and introduces polydimethylsiloxane with a terminal hydroxyl or carboxyl group as an esterification promoter. The use of composite bimetallic catalyst can improve the electronegativity while maintaining good hydrolysis resistance and dispersibility in the melt. Titanium-containing substances, especially when they are in an unsaturated coordination state, their empty orbitals (such as 3d orbitals) can act as electron pair acceptors, exhibiting Lewis acidity. The titanium metal center with Lewis acidity can accept the electron pair of the basic molecule containing a lone pair of electrons. The oxygen atoms on the PTA carboxyl group and the oxygen atoms on the active groups of the silicone terminal hydroxyl / carboxyl group both contain lone pair electrons, which are typical Lewis bases. When PTA and silicone molecules approach the titanium metal center at the same time, the empty orbitals of the titanium metal center can simultaneously chelate the oxygen atoms on the PTA carboxyl group and the oxygen atoms on the active groups of the silicone terminal, forming a stable four-membered ring or six-membered ring transition state. This chelation shortens the distance between the reactants and activates the carboxyl group, thereby significantly reducing the activation energy of the esterification reaction, which on the one hand greatly accelerates the main reaction rate, and on the other hand effectively suppresses the side reaction of generating cyclic oligomers by providing a more optimal reaction path, reducing impurity generation from the molecular source.

[0041] In addition, the traditional intermittent or semi-intermittent esterification kettle reaction has obvious "plateau period". That is, in the later stage of the reaction, as the PTA solid particles decrease, the reaction system transitions from heterogeneous to homogeneous, and the reaction rate sharply decreases. In this stage, the reaction is uneven, and local over-reaction or insufficient reaction occurs, leading to an increase in side reactions, a wide molecular weight distribution (PDI>2.5), a high content of oligomers, and high energy consumption and low efficiency.

[0042] The present application adopts a unique semi-continuous esterification reaction process with 40-60% built-in esterification raw material, continuously feeds new slurry, instantaneously mixes with high-temperature raw material in the kettle, and continuously outputs the completed esterification material from the bottom to directly enter the next process. This method creates and maintains an approximately homogeneous reaction environment. The pre-existing high-temperature esterification raw material in the reaction kettle provides an excellent pre-dispersion and pre-heating medium for the newly added PTA / EG slurry. The slurry is instantaneously dispersed and heated as soon as it enters the reaction kettle, rapidly converting the original heterogeneous solid-liquid reaction into a homogeneous liquid-liquid reaction. This completely eliminates the reaction lag and mass transfer resistance caused by the presence of PTA solid particles, greatly shortens or even eliminates the reaction plateau period, allowing the esterification reaction to maintain a high speed, stability, and uniformity throughout the process to achieve high conversion. This method suppresses side reactions, significantly reduces oligomer generation; the molecular chain growth environment is uniform, resulting in high-quality products with a narrower molecular weight distribution (PDI<2.2); and the reaction efficiency is improved, and energy consumption is significantly reduced.

[0043] The conventional polyester fiber molecular chain is composed of benzene rings and alkane chains, lacking affinity with non-aqueous media such as siloxane, making it difficult for dyes to diffuse smoothly from the medium to the interior of the fiber, resulting in low dye uptake. The existing technology often damages the regularity of the polyester molecular structure by introducing a third monomer through copolymerization modification, sacrificing its excellent mechanical properties and thermal stability.

[0044] The present application uses the above-mentioned active end group-containing siloxane compound as a reaction monomer to directly participate in the reaction in the esterification stage, and covalently bonds it to the polyester macromolecular chain. By using in-situ copolymerization and the principle of similar solubility, under the chelation guidance of a double metal catalyst, the hydroxyl / carboxyl group at the end of the siloxane reacts with the carboxyl group of PTA through condensation reaction, permanently and chemically bonding the entire siloxane segment to the polyester backbone, becoming part of the polymer molecular structure. This enables the modified fiber body to possess siloxane properties. During subsequent dyeing, the siloxane segment in the fiber and the siloxane dye bath medium based on the principle of similar solubility produce strong affinity, greatly promoting the swelling of the dye bath to the fiber and the diffusion and penetration of dye molecules into the interior of the fiber.

[0045] The application optimizes the molecular structure, ensures the mechanical properties of the fiber without deterioration due to modification while giving the fiber new dyeing functions, and especially improves the mechanical properties related to dyeing processing. By increasing the intrinsic viscosity of high-viscosity polyester chips to an industrial high standard (0.70~0.85 dL / g), the molecular basis for obtaining excellent mechanical properties of the fiber is ensured. By narrowing the molecular weight distribution index (PDI) to 2.2 or less, the homogenization and densification of the microstructure of the fiber are realized, which not only reduces oligomers from the source, but also directly optimizes and stabilizes the mechanical properties (especially strength and modulus). While successfully giving the fiber the new functions of "high dyeing rate in non-aqueous medium" and "no color spot", the mechanical properties of the fiber are ensured.

[0046] Advantages:

[0047] (1) The preparation method of the polyester fiber suitable for non-aqueous medium dyeing of the application effectively inhibits side reactions from the source through precise catalysis of a composite bimetallic catalyst and a homogeneous reaction environment of semi-continuous esterification, successfully controls the total content of oligomers in polyester chips below 0.6wt% (much lower than the traditional 1.5%~3.0%), and greatly reduces the proportion of cyclic trimers in oligomers, which fundamentally solves the core quality problems of dyeing color spots and white powder caused by the precipitation of oligomers in non-aqueous medium dyeing.

[0048] (2) The preparation method of the polyester fiber suitable for non-aqueous medium dyeing of the application shortens the esterification reaction time using a semi-continuous esterification process, makes the molecular chain growth environment more uniform, and the prepared polyester has a molecular weight distribution index (PDI) less than 2.2 (the traditional process is usually greater than 2.5); the narrower molecular weight distribution means that the fiber structure is more dense and uniform, which not only further reduces the tendency of oligomer precipitation, but also helps to improve the mechanical properties and dyeing uniformity of the fiber.

[0049] (3) The preparation method of the polyester fiber suitable for non-aqueous medium dyeing of the application creates a homogeneous environment for the base material technology, which keeps the esterification reaction rate at a high level, significantly shortens or even eliminates the time-consuming in the traditional process, reduces the overall esterification reaction time, and the energy consumption is expected to be reduced by 20~30%, improving the equipment utilization and production efficiency.

[0050] (4) The preparation method of the polyester fiber suitable for non-aqueous medium dyeing of the application does not need to rely on subsequent high-cost additives or processing, and provides a mature raw material solution for the textile printing and dyeing industry to realize water-saving, emission reduction, and energy-saving green production.

[0051] (5) The polyester fiber suitable for non-aqueous medium dyeing of the present application has siloxane segments permanently covalently bonded to the polyester molecular chain, which endows the fiber with the inherent property of "like dissolves like" with non-aqueous siloxane dyeing medium, so that the dye can quickly diffuse into the fiber interior, and the dyeing rate can be greater than 90% at a dyeing temperature of 110-130°C, which is better than the performance of traditional polyester in a high-temperature water bath (125-135°C).

[0052] (6) The polyester fiber suitable for non-aqueous medium dyeing of the present application has extremely low oligomer content, which avoids interference during dyeing, and in combination with uniform fiber structure, the dyed fabric has high color fastness, no color spots or stains, and the dyeing uniformity can reach 4-5 levels (the highest standard), and the product quality and one-time success rate are greatly improved. DETAILED DESCRIPTION

[0053] The present application will be further described in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0054] The performance indicators in the examples and comparative examples of the present application involve the following test methods:

[0055] Intrinsic viscosity: tested according to Method A in GB / T 14190-2008.

[0056] Oligomer content: tested according to GB / T 45710-2025.

[0057] Proportion of cyclic trimers in oligomers: TLC (thin layer chromatography) is used to separate the components in the oligomers, and then a dual-wavelength thin layer chromatography scanner is used for qualitative and quantitative analysis of the cyclic trimers.

[0058] Molecular weight distribution index: tested by GPC chromatograph, specifically, a solution (1.0 mg / ml) of the sample to be tested in hexafluoroisopropanol solvent is used for calibration before testing with polymethyl methacrylate (manufacturer: Sigma-Aldrich, model: 81501).

[0059] Dyeing rate: tested according to T / DLSHXH 017-2024.

[0060] Dyeing uniformity: visually evaluated by comparing the color difference between the dyed fabric and the standard sample with the aid of a gray sample card, and rated according to the color difference.

[0061] Example 1

[0062] A method for preparing polyester fibers suitable for non-aqueous medium dyeing, comprising the following steps:

[0063] (1) Preparation of raw materials:

[0064] terephthalic acid;

[0065] ethylene glycol;

[0066] tetrabutyl titanate;

[0067] hydroxyl-terminated polydimethylsiloxane II: number average molecular weight of 300 g / mol;

[0068] metal salt: zinc acetate;

[0069] composite bimetallic catalyst: complex of tetrabutyl titanate, ethylene glycol, hydroxyl-terminated polydimethylsiloxane II and metal salt; molar ratio of tetrabutyl titanate, ethylene glycol, hydroxyl-terminated polydimethylsiloxane II and metal salt is 1:2.75:0.25:1;

[0070] silicone group-containing esterification promoter: hydroxyl-terminated polydimethylsiloxane I, number average molecular weight of 400 g / mol;

[0071] (2) Using terephthalic acid and ethylene glycol as raw materials in a molar ratio of 1:1.08, adding the composite bimetallic catalyst and the silicone group-containing esterification promoter, and beating to form a slurry;

[0072] wherein the amount of the composite bimetallic catalyst added is 50 ppm of the mass of terephthalic acid in terms of the total mass of metal elements, and the amount of the silicone group-containing esterification promoter added is 1% of the mass of terephthalic acid;

[0073] (3) continuously feeding the slurry into an esterification reactor for esterification reaction, and when the esterification product accounts for 40% of the effective volume of the esterification reactor, continuously feeding the esterification product into a pre-polycondensation reactor and a final polycondensation reactor for polycondensation reaction while continuously feeding the slurry into the esterification reactor, to obtain a polyester melt;

[0074] Since the esterification product starts to be fed out, there is always 40% of the esterification product in the esterification reactor in terms of the effective volume; the liquid level in the esterification reactor is maintained constant by controlling the feeding amount and the discharging amount;

[0075] The conditions for esterification reaction are: temperature 245°C, pressure 0.35 MPa, and esterification rate 97%;

[0076] The conditions for polycondensation reaction are: pre-polycondensation temperature 265°C, pressure 8 kPa; final polycondensation temperature 265°C, and vacuum degree 80 Pa;

[0077] (4) The polyester melt with an intrinsic viscosity of 0.65 dL / g is sequentially cast into a tape and cut into granules, and then treated at 200°C for 15 hours under nitrogen protection to obtain high-viscosity polyester chips with an intrinsic viscosity of 0.7 dL / g;

[0078] (5) The high-viscosity polyester chips are dried at 120°C and melt-spun to obtain polyester fibers suitable for non-aqueous medium dyeing;

[0079] The process parameters for melt spinning are as follows: spinning temperature 285°C, draw ratio 3.5 times, and heat setting temperature 160°C.

[0080] The final polyester fibers suitable for non-aqueous medium dyeing have an oligomer content of 0.6 wt%, and the proportion of cyclic trimers in the oligomers is 60%; the molecular weight distribution index of the polyester fibers suitable for non-aqueous medium dyeing is 1.87, and the macromolecular chains thereof are bonded with siloxane segments;

[0081] The disperse dye is dissolved in decamethylcyclopentasiloxane to form a dye solution, and the polyester fibers suitable for non-aqueous medium dyeing are immersed in the dye solution and dyed at 110°C for 60 minutes; the dyeing rate of the polyester fibers suitable for non-aqueous medium dyeing to the disperse dye is 90%, the dyeing uniformity is grade 4, and there is no color spot phenomenon.

[0082] Comparative Example 1

[0083] A method for preparing polyester fibers suitable for non-aqueous medium dyeing is basically the same as in Example 1, except that the esterification promoter containing siloxane groups is omitted.

[0084] The final polyester fibers suitable for non-aqueous medium dyeing have an oligomer content of 0.8 wt%; the molecular weight distribution index of the polyester fibers suitable for non-aqueous medium dyeing is 2.1, and the macromolecular chains thereof are bonded with siloxane segments; the dyeing rate of the polyester fibers suitable for non-aqueous medium dyeing to the disperse dye is 85%, the dyeing uniformity is grade 4, and there is a color spot phenomenon.

[0085] Comparing Comparative Example 1 and Example 1, it can be found that the oligomer content of Comparative Example 1 increases, the dyeing rate decreases, and color spots appear. This is because, when the esterification promoter containing siloxane groups is not added, the number of molecules that can form a transition state with titanium metal centers in the reaction system is insufficient, which significantly weakens the catalytic synergy effect, making it difficult to effectively reduce the esterification activation energy, and the effect of shortening the esterification plateau period and inhibiting the generation of oligomers is greatly reduced. The reaction may still be trapped in the traditional "plateau period", and the oligomer content cannot be effectively reduced to below 0.6%. At the same time, there is a lack of sufficient siloxane segments inside the fibers to produce a strong "like dissolves like" effect with the dye bath medium, resulting in an unobvious improvement in dyeing affinity and an inability to break through 90% in dyeing rate.

[0086] Comparative Example 2

[0087] A method for preparing polyester fiber suitable for non-aqueous medium dyeing, which is substantially the same as example 1, except that in step (3), the "semi-continuous esterification process" in which the esterification reactor always contains 40% of the esterification product by effective volume is replaced by a "continuous process", i.e. the material continuously flows in two esterification reactors (i.e. the first esterification kettle and the second esterification kettle) in series, the material flows out from the bottom of the first esterification kettle and is pumped into the second esterification kettle, completing the whole process from esterification to polycondensation, and the internal reactor does not deliberately maintain a large amount of circulating bottom material; the material in each reactor is close to "plug flow", i.e. the newly added slurry has limited mixing with the reacted material, and the reactant concentration and reaction rate continuously change along the flow direction.

[0088] The final polyester fiber suitable for non-aqueous medium dyeing has an oligomer content of 0.85wt%; the polyester fiber suitable for non-aqueous medium dyeing has a molecular weight distribution index of 2.1, and the macromolecular chain thereof is bonded with a siloxane segment; the polyester fiber suitable for non-aqueous medium dyeing has a dye uptake of 80% for disperse dyes, a dyeing uniformity of 2 levels, and a color spot phenomenon.

[0089] Comparing example 1 with comparative example 2, it can be found that the oligomer content of comparative example 2 is increased, the dye uptake is decreased, the uniformity is poor and color spots appear, which is because the esterification kettle of comparative example 2 cannot effectively eliminate the esterification plateau, and the reaction is still intense and uneven at the beginning, leading to an increase in side reactions, a wide distribution of material residence time, long reaction time for some materials and short reaction time for some materials, resulting in uneven molecular chain length; when the new slurry enters the first esterification kettle, it still faces intense heterogeneous reaction, which leads to relatively poor consistency of the material and higher sensitivity to process fluctuations. The "continuous process" of comparative example 2 does not fundamentally change the nature of the heterogeneous reaction at the beginning of esterification.

[0090] Comparative example 3

[0091] A method for preparing polyester fiber suitable for non-aqueous medium dyeing, which is substantially the same as example 1, except that in step (3), the "semi-continuous esterification process" in which the esterification reactor always contains 40% of the esterification product by effective volume is replaced by a "batch process", i.e. all raw materials (such as PTA, EG, composite bimetallic catalyst and siloxane promoter) of one batch are added into the same reactor at one time, and all steps from slurry preparation, esterification to early polycondensation are completed in the same reactor; the material does not exchange with the outside during the reaction; when the reaction reaches the predetermined index (such as esterification rate), the whole reactor material is discharged and sent to the next process; then the reactor is cleaned and the next batch cycle begins.

[0092] The polyester fiber for non-aqueous medium dyeing has an oligomer content of 0.95wt%, a molecular weight distribution index of 2.2, and a macromolecular chain bonded with a siloxane segment; the dyeing rate of the polyester fiber for non-aqueous medium dyeing to disperse dyes is 80%, the dyeing uniformity is 2 levels, and there is a color spot phenomenon.

[0093] Comparing the comparative example 3 and the example 1, it can be found that the oligomer content of the comparative example 3 is increased, the dyeing rate is reduced, the uniformity is poor, and there is a color spot phenomenon, because the traditional batch esterification kettle of the comparative example 3 cannot shorten the esterification plateau, the reaction efficiency is low, the energy consumption is high, and the side reaction time is long, so that the oligomer content cannot be reduced to below 0.6%, or even higher; the reactant concentration, temperature and viscosity continuously change in the process, the molecular chain grows unevenly, the fiber quality is unstable, the color difference is serious within and between batches during dyeing, and the uniformity of 4-5 levels cannot be guaranteed; the fiber structure is loose and uneven, which provides a large number of channels and places for the late oligomer precipitation, and every batch of feeding and reaction of the slight difference will cause the fluctuation of the quality of the final product.

[0094] Comparative example 4

[0095] A method for preparing a polyester fiber for non-aqueous medium dyeing, which is basically the same as the example 1, except that the "semi-continuous esterification reaction process" in which 40% of the esterification product is always stored in the esterification reactor is replaced by a "semi-batch process", that is, one kind of material is added at one time, and another kind of material is continuously added, but the product is not discharged during the reaction process, the specific process is as follows: 60% of PTA, EG, composite bimetallic catalyst and siloxane promoter are added into the reactor, and the reaction is started; during the reaction process, the remaining 40% of PTA, EG, composite bimetallic catalyst and siloxane promoter are continuously added into the reactor which is reacting; during the whole esterification reaction stage, the reactor only inputs and does not output, and no material is continuously transported to the polycondensation process; when all the materials are added and the target esterification rate is reached, the whole reactor material is discharged and sent to the next process, and then the next production cycle is started.

[0096] The polyester fiber for non-aqueous medium dyeing has an oligomer content of 0.88wt%, a molecular weight distribution index of 2.3, and a macromolecular chain bonded with a siloxane segment; the dyeing rate of the polyester fiber for non-aqueous medium dyeing to disperse dyes is 80%, the dyeing uniformity is 2 levels, and there is a color spot phenomenon.

[0097] Comparative Example 4 and Example 1 are compared, it can be found that the oligomer content of Comparative Example 4 is increased, the dyeing rate is reduced, the dyeing uniformity is poor and color spots appear, because Comparative Example 4 cannot realize a true homogeneous platform, the reaction environment is always fluctuating, the reactant concentration, system viscosity and liquid level are continuously changing, it is a transient process; the materials added later experience different reaction paths from the early materials, resulting in a wide molecular weight distribution (PDI) and failing to stably reach a level of <2.2; although it is better than the whole batch process of Comparative Example 3, the concentration of by-product in the reaction system will accumulate over time and cannot be removed in time; the oligomer content control effect is decreased and it is difficult to stably be lower than 0.6wt%, and there is a large difference between batches; the materials of the early reaction and the late reaction are different, resulting in that the materials in the single reactor are not uniform; during spinning and dyeing, different parts of the same batch of fibers may show differences, and the dyeing uniformity and stability without color spots cannot be guaranteed; the whole feeding, reaction and unloading cycle needs to be completed, and the efficiency is much lower than that of the continuous process.

[0098] Example 2

[0099] A preparation method of a polyester fiber suitable for non-aqueous medium dyeing, the specific steps are as follows:

[0100] (1) Preparation of raw materials:

[0101] terephthalic acid;

[0102] ethylene glycol;

[0103] titanium tetrabutoxide;

[0104] hydroxyl-terminated polydimethylsiloxane: number average molecular weight 800 g / mol;

[0105] metal salt: magnesium acetate;

[0106] composite bimetallic catalyst: complex of titanium tetrabutoxide, ethylene glycol, hydroxyl-terminated polydimethylsiloxane and metal salt; the molar ratio of titanium tetrabutoxide, ethylene glycol, hydroxyl-terminated polydimethylsiloxane and metal salt is 1:3:0.25:1;

[0107] silicone group-containing esterification promoter: carboxyl-terminated polydimethylsiloxane, number average molecular weight 2000 g / mol;

[0108] (2) Terephthalic acid and ethylene glycol with a molar ratio of 1:1.2 are used as raw materials, a composite bimetallic catalyst and a silicone group-containing esterification promoter are added, and a slurry is formed by beating;

[0109] The addition amount of the composite bimetallic catalyst is 180 ppm of the mass of terephthalic acid based on the total mass of metal elements, and the addition amount of the silicone group-containing esterification promoter is 2% of the mass of terephthalic acid;

[0110] (3) continuously feeding the slurry into the esterification reactor to perform esterification reaction, and when the esterification product accounts for 60% of the effective volume of the esterification reactor, continuously feeding the slurry into the esterification reactor while sequentially feeding the esterification product into the pre-polycondensation reactor and the final polycondensation reactor to perform polycondensation reaction, so as to obtain polyester melt;

[0111] Since the esterification product starts to be fed out, the esterification reactor always contains the esterification product accounting for 60% of the effective volume; the liquid level in the esterification reactor is maintained constant by controlling the feeding amount and the discharging amount;

[0112] The esterification reaction is performed under the conditions of temperature 250°C and pressure 0.2 MPa, and the esterification rate is 97%;

[0113] The polycondensation reaction is performed under the conditions of pre-polycondensation temperature 268°C and pressure 6 kPa, and final polycondensation temperature 270°C and vacuum degree 50 Pa;

[0114] (4) the polyester melt with intrinsic viscosity 0.6 dL / g is sequentially subjected to casting and pelletizing, and then treated at 220°C for 8 hours under nitrogen protection, so as to obtain high-viscosity polyester chip with intrinsic viscosity 0.85 dL / g;

[0115] (5) the high-viscosity polyester chip is dried at 100°C, and then melt-spun to obtain polyester fiber suitable for non-aqueous medium dyeing;

[0116] The process parameters of melt spinning are as follows: spinning temperature 288°C, draw ratio 4 times, and heat setting temperature 165°C.

[0117] The oligomer content in the finally obtained polyester fiber suitable for non-aqueous medium dyeing is 0.6 wt%, and the proportion of cyclic trimer in the oligomer is 62%;

[0118] The molecular weight distribution index of the polyester fiber suitable for non-aqueous medium dyeing is 1.75, and the macromolecular chain thereof is bonded with siloxane segment; the disperse dye is dissolved in octamethylcyclotetrasiloxane to form a dye solution, and the polyester fiber suitable for non-aqueous medium dyeing is immersed in the dye solution and dyed at 115°C for 55 minutes; the dyeing rate of the polyester fiber suitable for non-aqueous medium dyeing to the disperse dye is 97%, the dyeing uniformity is grade 5, and there is no color spot phenomenon.

[0119] Example 3

[0120] A preparation method of polyester fiber suitable for non-aqueous medium dyeing, and the specific steps are as follows:

[0121] (1) preparation of raw materials:

[0122] terephthalic acid;

[0123] ethylene glycol;

[0124] Tetrabutyl titanate;

[0125] Propylene glycol;

[0126] Hydroxy-terminated polydimethylsiloxane II: number average molecular weight of 500 g / mol;

[0127] Metal salt: zinc acetate;

[0128] Composite bimetallic catalyst: complex of tetrabutyl titanate, propylene glycol, hydroxy-terminated polydimethylsiloxane II and metal salt; molar ratio of tetrabutyl titanate, propylene glycol, hydroxy-terminated polydimethylsiloxane II and metal salt is 1:2.75:0.5:1;

[0129] Siloxane group-containing esterification promoter: hydroxy-terminated polydimethylsiloxane I, number average molecular weight of 800 g / mol;

[0130] (2) terephthalic acid and ethylene glycol as raw materials in a molar ratio of 1:1.12, composite bimetallic catalyst and siloxane group-containing esterification promoter are added to form a slurry;

[0131] The amount of composite bimetallic catalyst added is 100 ppm of terephthalic acid in terms of total metal element mass, and the amount of siloxane group-containing esterification promoter added is 3% of terephthalic acid;

[0132] (3) continuously feeding the slurry into an esterification reactor to perform esterification reaction, when the esterification product accounts for 45% of the effective volume of the esterification reactor, continuously feeding the slurry into the esterification reactor while sequentially feeding the esterification product into a pre-polycondensation reactor and a final polycondensation reactor to perform polycondensation reaction, and obtaining a polyester melt;

[0133] From the beginning of feeding the esterification product, there is always 45% of the esterification product in the esterification reactor in terms of effective volume; the liquid level in the esterification reactor is maintained constant by controlling the feeding amount and discharging amount;

[0134] The conditions of esterification reaction are: temperature 255°C, pressure 0.1 MPa, esterification rate 98%;

[0135] The conditions of polycondensation reaction are: pre-polycondensation temperature 270°C, pressure 5 kPa; final polycondensation temperature 270°C, vacuum degree 40 Pa;

[0136] (4) the polyester melt with intrinsic viscosity of 0.7 dL / g is sequentially cast into a belt, cut into particles, and then treated at 205°C for 13 hours under nitrogen protection, to obtain high-viscosity polyester chips with intrinsic viscosity of 0.75 dL / g;

[0137] (5) the high-viscosity polyester chips are dried at 120°C, melt-spun to obtain polyester fibers suitable for non-aqueous medium dyeing;

[0138] The process parameters of melt spinning are as follows: spinning temperature 290℃, draw ratio 4.5 times, heat setting temperature 170℃.

[0139] The oligomer content of the polyester fiber suitable for non-aqueous medium dyeing is 0.5wt%, and the proportion of cyclic trimers in the oligomers is 65%; the molecular weight distribution index of the polyester fiber suitable for non-aqueous medium dyeing is 1.88, and the macromolecular chain thereof is bonded with a siloxane segment;

[0140] The disperse dye is dissolved in decamethylcyclopentasiloxane to form a dye solution, and the polyester fiber suitable for non-aqueous medium dyeing is immersed in the dye solution and dyed at 120℃ for 50 minutes; the dyeing rate of the polyester fiber suitable for non-aqueous medium dyeing to the disperse dye is 94%, the dyeing uniformity is 5 levels, and there is no color spot phenomenon.

[0141] Example 4

[0142] A preparation method of a polyester fiber suitable for non-aqueous medium dyeing, the specific steps are as follows:

[0143] (1) Preparation of raw materials:

[0144] terephthalic acid;

[0145] ethylene glycol;

[0146] titanium tetrabutoxide;

[0147] pentanediol;

[0148] hydroxyl-terminated polydimethylsiloxane: number average molecular weight 300g / mol;

[0149] metal salt: magnesium acetate;

[0150] composite bimetallic catalyst: complex of titanium tetrabutoxide, pentanediol, hydroxyl-terminated polydimethylsiloxane and metal salt; the molar ratio of titanium tetrabutoxide, pentanediol, hydroxyl-terminated polydimethylsiloxane and metal salt is 1:2.75:0.25:1.25;

[0151] siloxane group-containing esterification promoter: carboxyl-terminated polydimethylsiloxane, number average molecular weight 1200g / mol;

[0152] (2) Terephthalic acid and ethylene glycol with a molar ratio of 1:1.14 are used as raw materials, and a composite bimetallic catalyst and a siloxane group-containing esterification promoter are added to form a slurry;

[0153] The addition amount of the composite bimetallic catalyst is 130ppm of the total mass of metal elements based on the mass of terephthalic acid, and the addition amount of the siloxane group-containing esterification promoter is 4% of the mass of terephthalic acid.

[0154] (3) continuously feeding the slurry into the esterification reactor to perform esterification reaction, and when the esterification product accounts for 50% of the effective volume of the esterification reactor, continuously feeding the slurry into the esterification reactor while sequentially feeding the esterification product into the pre-polycondensation reactor and the final polycondensation reactor to perform polycondensation reaction, so as to obtain polyester melt;

[0155] Since the esterification product starts to be fed out, the esterification reactor always contains the esterification product accounting for 50% of the effective volume; the liquid level in the esterification reactor is maintained constant by controlling the feeding amount and the discharging amount;

[0156] The esterification reaction is performed under the conditions of temperature 260°C and pressure 0.05 MPa, and the esterification rate is 98%;

[0157] The polycondensation reaction is performed under the conditions of pre-polycondensation temperature 272°C and pressure 4 kPa, and final polycondensation temperature 272°C and vacuum degree 60 Pa;

[0158] (4) the polyester melt with intrinsic viscosity 0.67 dL / g is sequentially subjected to casting and pelletizing, and then treated at 210°C for 11 hours under nitrogen protection, so as to obtain high-viscosity polyester chip with intrinsic viscosity 0.8 dL / g;

[0159] (5) the high-viscosity polyester chip is dried at 100°C and melt-spun to obtain polyester fiber suitable for non-aqueous medium dyeing;

[0160] The process parameters of melt spinning are as follows: spinning temperature 293°C, draw ratio 4.5 times, and heat setting temperature 175°C.

[0161] The oligomer content in the finally obtained polyester fiber suitable for non-aqueous medium dyeing is 0.5 wt%, and the proportion of cyclic trimer in the oligomer is 60%; the molecular weight distribution index of the polyester fiber suitable for non-aqueous medium dyeing is 1.91, and the macromolecular chain thereof is bonded with siloxane segment;

[0162] The disperse dye is dissolved in octamethylcyclotetrasiloxane to form a dye solution, and the polyester fiber suitable for non-aqueous medium dyeing is immersed in the dye solution and dyed at 125°C for 40 minutes; the dyeing rate of the polyester fiber suitable for non-aqueous medium dyeing to the disperse dye is 97%, the dyeing uniformity is grade 4, and there is no color spot phenomenon.

[0163] Example 5

[0164] A preparation method of polyester fiber suitable for non-aqueous medium dyeing, the specific steps are as follows:

[0165] (1) preparation of raw materials:

[0166] terephthalic acid;

[0167] ethylene glycol;

[0168] tetrabutyl titanate;

[0169] pentanediol;

[0170] hydroxyl-terminated polydimethylsiloxane II: number average molecular weight of 800 g / mol;

[0171] metal salt: zinc acetate;

[0172] composite bimetallic catalyst: complex of tetrabutyl titanate, pentanediol, hydroxyl-terminated polydimethylsiloxane II and metal salt; molar ratio of tetrabutyl titanate, pentanediol, hydroxyl-terminated polydimethylsiloxane II and metal salt is 1:3:0.5:1.25;

[0173] siloxane group-containing esterification promoter: hydroxyl-terminated polydimethylsiloxane I, number average molecular weight of 1600 g / mol;

[0174] (2) terephthalic acid and ethylene glycol as raw materials in a molar ratio of 1:1.16, composite bimetallic catalyst and siloxane group-containing esterification promoter are added to form a slurry;

[0175] wherein the composite bimetallic catalyst is added in an amount of 150 ppm of terephthalic acid in terms of total mass of metal elements, and the siloxane group-containing esterification promoter is added in an amount of 2% of terephthalic acid;

[0176] (3) continuously feeding the slurry into an esterification reactor to perform esterification reaction, when the esterification product accounts for 55% of the effective volume of the esterification reactor, continuously feeding the slurry into the esterification reactor while sequentially feeding the esterification product into a pre-polycondensation reactor and a final polycondensation reactor to perform polycondensation reaction, and obtaining a polyester melt;

[0177] Since the esterification product starts to be fed out, the esterification reactor always has 55% of the effective volume of the esterification product; the liquid level in the esterification reactor is maintained constant by controlling the feeding amount and the discharging amount;

[0178] The conditions of the esterification reaction are: temperature 245°C, pressure 0.35 MPa, and esterification rate 97%;

[0179] The conditions of the polycondensation reaction are: pre-polycondensation temperature 275°C, pressure 2 kPa; final polycondensation temperature 275°C, and vacuum degree 80 Pa;

[0180] (4) the polyester melt with intrinsic viscosity of 0.64 dL / g is sequentially cast into a belt, cut into particles, and then treated at 215°C for 10 hours under nitrogen protection, to obtain a high-viscosity polyester chip with intrinsic viscosity of 0.82 dL / g;

[0181] (5) The high-viscosity polyester chip is dried at 120°C and melt-spun to obtain polyester fiber suitable for non-aqueous medium dyeing;

[0182] The process parameters of melt spinning are as follows: spinning temperature 295°C, draft ratio 4.5 times, and heat setting temperature 180°C.

[0183] The oligomer content of the finally obtained polyester fiber suitable for non-aqueous medium dyeing is 0.6 wt%, and the proportion of cyclic trimers in the oligomers is 68%; the molecular weight distribution index of the polyester fiber suitable for non-aqueous medium dyeing is 1.85, and the macromolecular chains thereof are bonded with siloxane segments;

[0184] The disperse dye is dissolved in decamethylcyclopentasiloxane to form a dye solution, and the polyester fiber suitable for non-aqueous medium dyeing is immersed in the dye solution and dyed at 130°C for 30 minutes; the dyeing rate of the polyester fiber suitable for non-aqueous medium dyeing to the disperse dye is 95%, the dyeing uniformity is grade 5, and there is no color spot phenomenon.

Claims

1. A process for the production of polyester fibers suitable for dyeing in nonaqueous media, characterized in that: The terephthalic acid and ethylene glycol are used as raw materials, a composite bimetallic catalyst and an esterification promoter containing siloxane groups are added, and pulp is formed; then the pulp is continuously fed into an esterification reactor for esterification reaction, when the esterification product accounts for 40-60% of the effective volume of the esterification reactor, the esterification product is sequentially fed into a pre-polycondensation reactor and a final polycondensation reactor for polycondensation reaction while the pulp is continuously fed into the esterification reactor, and a polyester melt is obtained; finally, the polyester melt is sequentially subjected to casting, granulation and solid-phase tackification to obtain high-viscosity polyester chips, and then melt spinning is performed to obtain polyester fibers suitable for non-aqueous medium dyeing; The composite bimetallic catalyst is a titanium-zinc bimetallic catalyst or a titanium-magnesium bimetallic catalyst; The esterification promoter containing siloxane groups is hydroxyl-terminated polydimethylsiloxane I or carboxyl-terminated polydimethylsiloxane; the number average molecular weight of the esterification promoter containing siloxane groups is 400-2000 g / mol; The intrinsic viscosity of the high-viscosity polyester chips is 0.70-0.85 dL / g; From the start of feeding the esterification product, the esterification reactor always contains 40-60% of the esterification product based on the effective volume; The oligomer content of the polyester fibers suitable for non-aqueous medium dyeing is less than 0.6 wt%, and the proportion of cyclic trimers in the oligomers is not less than 60%; The polyester fibers suitable for non-aqueous medium dyeing have an up-take rate of disperse dyes of not less than 90%, a dyeing uniformity of 4-5 levels, and no color spot phenomenon.

2. The method for producing polyester fiber suitable for non-aqueous medium dyeing according to claim 1, characterized by, The molar ratio of terephthalic acid to ethylene glycol is 1:1.08-1.20, the addition amount of the composite bimetallic catalyst is 50-180 ppm of the mass of terephthalic acid based on the total mass of metal elements, and the addition amount of the esterification promoter containing siloxane groups is 1.0-4.0% of the mass of terephthalic acid.

3. The method of claim 1, wherein the polyester fiber is prepared by the steps of: (1) mixing a polyester resin, a dye, and a solvent to prepare a mixture; (2) extruding the mixture to prepare a fiber; and (3) drying the fiber. The composite bimetallic catalyst is a complex of tetrabutyl titanate, a dihydric alcohol, hydroxyl-terminated polydimethylsiloxane II and a metal salt; The dihydric alcohol is an aliphatic dihydric alcohol with a carbon atom number of 2-5, the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane II is 300-800 g / mol, and the metal salt is zinc acetate or magnesium acetate; The molar ratio of tetrabutyl titanate, dihydric alcohol, hydroxyl-terminated polydimethylsiloxane II and metal salt is 1:2.75-3:0.25-0.5:1-1.

25.

4. The method of claim 1, wherein the polyester fiber is prepared by the steps of: (1) mixing a polyester resin, a dye, and a solvent to prepare a mixture; (2) extruding the mixture to form a fiber; and (3) drying the fiber. The liquid level in the esterification reactor is maintained constant by controlling the feed and discharge amounts.

5. The method of claim 1, wherein the polyester fiber is prepared by the steps of: (1) mixing a polyester resin, a dye, and a solvent to prepare a mixture; (2) extruding the mixture to form a fiber; and (3) drying the fiber. The conditions of the esterification reaction are: temperature 245-260°C, pressure 0.05-0.35 MPa, and esterification rate not less than 97%; The conditions of the polycondensation reaction are: pre-polycondensation temperature 265-275°C, pressure 2-8 kPa; final polycondensation temperature 265-275°C, and vacuum degree less than or equal to 80 Pa.

6. The method for preparing polyester fibers suitable for dyeing in non-aqueous media according to claim 1, characterized in that, The intrinsic viscosity of the polyester melt is 0.60-0.70 dL / g.

7. The method of claim 1, wherein the polyester fiber is prepared by the steps of: (1) mixing a polyester resin, a dye, and a solvent to prepare a mixture; (2) extruding the mixture to form a fiber; and (3) drying the fiber. The conditions of the solid-phase tackification are: treatment at 200-220°C for 8-15 hours under nitrogen protection.

8. The method for preparing polyester fibers suitable for dyeing in non-aqueous media according to claim 1, characterized in that, The process parameters of the melt spinning are: spinning temperature 285-295°C, draw ratio 3.5-4.5 times, and heat setting temperature 160-180°C.

9. Polyester fibers suitable for dyeing in non-aqueous media, prepared by the process according to any one of claims 1 to 8, characterized in that: The oligomer content of the polyester fibers suitable for non-aqueous medium dyeing is less than 0.6 wt%, and the proportion of cyclic trimers in the oligomers is not less than 60%; The polyester fibers suitable for non-aqueous medium dyeing have an up-take rate of disperse dyes of not less than 90%, a dyeing uniformity of 4-5 levels, and no color spot phenomenon. The polyester fiber suitable for non-aqueous medium dyeing has a molecular weight distribution index less than 2.2 and a siloxane chain segment bonded on the macromolecular chain.

10. The polyester fiber suitable for dyeing in a non-aqueous medium according to claim 9, characterized by, The dispersion dye is dissolved in the siloxane medium to form a dye solution, and the polyester fiber suitable for non-aqueous medium dyeing is immersed in the dye solution and dyed at 110-130 ℃ for 30-60 minutes. The siloxane medium is decamethylcyclopentasiloxane or octamethylcyclotetrasiloxane. The polyester fiber suitable for non-aqueous medium dyeing has an up-take rate of the dispersion dye not less than 90%, a dyeing uniformity of 4-5 grades and no color spot phenomenon.