A polyester fiber with low content of surface oligomers and preparation method thereof

Abstract

The invention discloses a polyester fiber with low content of surface oligomers and a preparation method thereof, belonging to the technical field of polyester fiber preparation. PTA and EG are used as raw materials, BHET is generated by esterification reaction, and PET is obtained by polycondensation reaction under the action of a catalyst; PET is then spun and post-treated to prepare polyester fiber; in the esterification reaction stage, EG / PTA is controlled to be 1.05-1.10, and the final polycondensation reaction temperature is 270-280°C; the total stretching multiple of the pre-spinning is 4.3±0.2 times; the total stretching multiple of the post-spinning stage is 4.0±0.2 times, the primary stretching multiple is ≥90%, and the temperature is 80±5°C; the secondary stretching temperature is 180±5°C; the temperature of the post-spinning step-by-step drawing and tense heat setting process is 70°C-185°C; and the heat setting time is 40±5s. The problem of oligomer precipitation on the surface of polyester fiber is solved by improving the key processes and parameters in the preparation process.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, specifically to the technical field of polyester fiber preparation, and in particular relates to a polyester fiber with a low content of surface oligomers and a preparation method thereof. Background Art

[0002] Polyethylene terephthalate (PET) staple fiber is a fiber widely used in the field of clothing or textiles, with many advantages such as excellent performance, cheap raw materials, and rich varieties. However, due to the excessive number of parameters that need to be regulated in the preparation process, the complex preparation process, and the multi-dimensional processing temperature, oligomers are easily precipitated on the surface of polyethylene terephthalate, forming white powder that can fall off in subsequent processes such as spinning and dyeing, which has a great adverse impact on production safety and product quality.

[0003] In order to solve the problem of white powder precipitation on the surface of PET, technicians in this field have proposed many ideas, such as the Chinese patent "Polyester fiber oligomer inhibitor" (CN1289749C), which discloses a polyester fiber oligomer inhibitor, including one or more ester compounds, selected from ester compounds of propylene oxide adducts of polyols and alkyl or alkenyl fatty acids, the ester compounds are obtained by the transesterification reaction of propylene oxide adducts of polyols and animal or vegetable oils and fats "containing alkyl and / or alkenyl fatty acids". The invention basically solves the problem caused by geopolymers through the idea of ​​adding external inhibitors, and has no adverse effect on the fiber dyeing ability. Another example is the invention named "A method for reducing the content of geopolymers in polyester fibers"

[0004] (CN108130615A) Chinese patent discloses a method for reducing the oligomer content in polyester fibers. First, a branched diol chain segment is introduced into the molecular chain of polyester to obtain a modified polyester. Then, in the cooling process of spinning the modified polyester to prepare the polyester fiber, the longitudinal height is kept unchanged, the cross-sectional area of ​​the slow cooling chamber is increased, and the slow cooling chamber adopts a heat preservation method to maintain the plate surface temperature of the spinneret. The structural formula of the branched diol is as follows: In the formula, R1 and R2 are each independently selected from a linear alkylene group having 1 to 3 carbon atoms, R3 is selected from an alkyl group having 1 to 5 carbon atoms, and R4 is selected from an alkyl group having 2 to 5 carbon atoms. The above-mentioned prior arts all solve the problem of excessive oligomer content on the surface of polyester fibers by adding auxiliary agents such as modifiers or inhibitors. However, the addition of modifiers or inhibitors will inevitably make the process more complicated, and the remaining process steps or parameters also need to be improved and adjusted in a targeted manner, and the structure or performance of the product will change to a certain extent. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention proposes a polyester fiber with low content of surface oligomers and a preparation method thereof, and solves the problem of oligomer precipitation on the surface of polyester fiber by improving key processes and parameters in the polyester fiber preparation process.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] One of the technical schemes of the present invention is to provide a method for preparing polyester fiber with low content of surface oligomers. The method uses terephthalic acid (PTA) and excess ethylene glycol (EG) as raw materials, generates bis(hydroxyethyl) terephthalate (BHET) through esterification reaction, and then undergoes polycondensation reaction under the action of a catalyst to obtain high-polymerization degree polyethylene terephthalate; the polyethylene terephthalate is then spun and post-treated to obtain polyester fiber; wherein, in the esterification reaction stage, the molar ratio of ethylene glycol to terephthalic acid is EG / PTA=1.05-1.10, and in the final polycondensation reaction stage, the reaction temperature is 270-280°C.

[0008] The chemical reaction routes of the esterification reaction and polycondensation reaction of the present invention are as follows:

[0009]

[0010] The stretching process in the pre-spinning stage and the post-spinning process stage adopts multi-roller stretching; wherein, the total stretching multiple of the pre-spinning stretching process is 4.3±0.2 times; the total stretching multiple of the post-spinning stretching process is 4.0±0.2 times, and the primary stretching multiple is ≥90%; the primary stretching temperature is 80±5℃; the secondary stretching temperature is 180±5℃; the corresponding water vapor pressure is 1.0±0.13MPa. The temperature of the step-by-step drawing and tense heat setting process in the post-spinning process stage is 70℃~185℃; the corresponding maximum water vapor pressure is 1.13MPa, and the heat setting time is controlled at 40±5s.

[0011] Under the condition of other constant conditions, the increase of reaction temperature can accelerate the reaction speed. If a polyester with an intrinsic viscosity of 0.650 is to be obtained, the esterification temperature should be higher than 240°C, otherwise not only the reaction time of esterification and polycondensation needs to be prolonged, but also the obtained product has a low melting point, a high DEG content, and a poor hue. However, the esterification temperature cannot be too high, otherwise it will accelerate the side reaction and affect the quality. Therefore, as a further preferred embodiment of the present invention, in the esterification reaction stage, the optimal molar ratio of ethylene glycol and terephthalic acid is EG / PTA=1.06, and in the final polycondensation reaction stage, the optimal reaction temperature is 275°C.

[0012] As a further preferred embodiment of the present invention, the final polycondensation reaction stage further includes the step of adding a stabilizer; adding a stabilizer is an important means of regulating the formation and precipitation of oligomers in the polymerization process, and the stabilizer of the present invention is a phosphate stabilizer; the amount of the stabilizer added is 1.0 to 1.8×10 of the amount of terephthalic acid. -4 times.

[0013] As a further preferred embodiment of the present invention, the phosphate series stabilizer includes triphenyl phosphate, trimethyl phosphate, triaryl phosphate, nitrophenyl phosphate, tetraisopropyl methylene diphosphate, dibutyl isobutyl phosphate, triethyl phosphonoacetate or trimethyl phosphonoacetate.

[0014] In the early stage of esterification, it is a solid-liquid phase reaction, so the properties of the EG / PTA slurry entering the first esterification reactor have a great influence on the esterification reaction. PTA with good slurry properties has a lower viscosity at the same EG / PTA molar ratio, and PTA with good stability is not easy to agglomerate after slurrying. Obviously, these two characteristics of PTA have practical significance for reducing stirring power, improving esterification reaction speed and reaction uniformity and product quality. Within a certain range, the average particle size increases, and the slurry property and stability are improved. The intrinsic quality of PTA, such as water content and 4-CBA (p-carboxybenzaldehyde) content, has an impact on the esterification reaction and product quality. Therefore, as a further preference of the present invention, the more suitable average particle size of PTA in the present invention is between 120 and 130 μm.

[0015] In order to maintain an appropriate EG / PTA molar ratio, the esterification reaction is usually carried out under pressure. Increasing the pressure speeds up the reaction and shortens the esterification time, but at the same time, the by-products in the esterification product also increase. In addition, the pressure reaction places more stringent requirements on the reaction equipment. The esterification effluent is not conducive to volatilization due to the pressure effect. Therefore, the reaction pressure conditions need to be reasonably selected according to the characteristics of various devices. The reaction pressure used in the present invention is generally 50KPa.

[0016] The key to the esterification reaction is to make the esterification rate of the material in the first esterification reactor reach 86-89%, and the esterification rate of the material entering the pre-shrinking reactor reach 96-97%. For this purpose, there must be sufficient reaction time, but the reaction time is closely related to the reaction temperature, the material level of the reactor, the MR of the slurry and other parameters. Moreover, too long reaction time will easily lead to poor product quality, so the reaction time should not be too long. Generally speaking, under the premise of meeting the esterification rate, the shorter the reaction time, the better the product quality, and for the production process of the same equipment, shortening the reaction time will increase the production capacity.

[0017] As a further preference of the present invention, the spinning stage includes a pre-spinning process stage and a post-spinning process stage; during cooling and solidification in the pre-spinning process stage, ring blowing or side blowing is adopted, the temperature is 25±2°C, and the wind speed is 0.5-0.6m / s.

[0018] As a further preferred embodiment of the present invention, the catalyst is antimony glycolate or SbAc3; the mass of the added catalyst varies depending on the type of catalyst. The amount of the added catalyst in the present invention is 1.8 to 2.4×10 -4 mol / mol terephthalic acid, that is, the amount of terephthalic acid is 1.8 to 2.4 × 10 -4 times.

[0019] As a further preferred embodiment of the present invention, when the polyethylene terephthalate is conveyed before spinning, the conveying and parking temperatures are kept below 280° C., and the conveying and parking times are as short as possible.

[0020] As a further preferred embodiment of the present invention, the esterification reaction stage further includes a step of adding an esterification catalyst; the esterification catalyst is an organic antimony, preferably ethylene glycol antimony or antimony acetate, more preferably ethylene glycol antimony. Since PTA itself can generate H + , plays a catalytic role, so the esterification reaction itself can proceed without a catalyst reaction, but the esterification reaction is also accompanied by a partial pre-shrinkage reaction to generate 3-5 polymers and release a molecule of EG to supplement the EG consumed by the esterification reaction. Therefore, only when the partial pre-shrinkage reaction proceeds smoothly can it provide enough EG to meet the needs of the esterification reaction and make the esterification reaction proceed smoothly. The smoother the pre-shrinkage reaction proceeds, the higher the MR (relative molecular mass) of the product of the esterification reaction will be, which is very beneficial to increasing the rate of the esterification reaction. Therefore, in the esterification reaction, especially under high load, the catalyst required for the polycondensation reaction also has a catalytic effect on the formation of 3-5 polymers in the esterification reaction stage.

[0021] As a further preferred embodiment of the present invention, during the whole process of preparing the polyester fiber, the ambient temperature of the production workshop is maintained at no more than 30°C.

[0022] The technical solution of the second aspect of the present invention is to provide a polyester fiber with a low content of surface oligomers prepared by the above method.

[0023] The present invention studies the relationship between powder shedding performance and surface oligomer content, and determines the idea of ​​solving the problem of polyester fiber powder shedding by providing a preparation method with low surface oligomer content. The present invention designs a preparation method for polyester fiber with low surface oligomer content by studying the influence of each process stage on the formation of oligomers. The method mainly adjusts the esterification reaction stage, the molar ratio of ethylene glycol and terephthalic acid is EG / PTA=1.05-1.10; adds a catalyst and adjusts the reaction temperature to 270-280°C in the final polycondensation reaction stage; and controls the stretching multiple of the pre-spinning stage and the temperature of the post-spinning stage in the spinning stage. The purpose of reducing the surface oligomer content of polyester fiber can be achieved.

[0024] In addition, the oligomer content on the surface of polyester fibers was further reduced by adding stabilizers and esterification catalysts during the reaction and regulating the temperature of each process in the spinning process.

[0025] The preparation method of the present invention has simple process, high efficiency and convenience, and effectively improves the subsequent application performance of the polyester fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the polyester fiber prepared in Example 1;

[0027] Figure 2 This is a scanning electron microscope image of the polyester fiber prepared in Comparative Example 1;

[0028] Figure 3 This is a scanning electron microscope image of the polyester fiber prepared in Comparative Example 2. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0031] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0032] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0033] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] All raw materials in the following examples of the present invention are commercially available, wherein the average particle size of PTA is between 120 and 130 μm.

[0035] The preparation method of polyester fiber in the following examples adopts a five-reactor reaction system, including two esterification reactors (a primary esterification reactor and a secondary esterification reactor) and three polymerization reactors (a primary polymerization reactor, a secondary polymerization reactor and a tertiary polymerization reactor). The stirring methods used in the three polymerization reactors are initial polymerization frame stirring, polymerization cage stirring and final polymerization cage stirring. The temperature of the entire production workshop is controlled at 25°C to 30°C.

[0036] Technical details not described in the following examples may be selected conventionally in the art, and are not essential to the present invention, and will not be described in detail in the examples.

[0037] Example 1

[0038] A method for preparing polyester fiber with low content of surface oligomers comprises the following steps:

[0039] Step 1:

[0040] S1. According to EG / PTA = 1.06 (molar ratio), weigh terephthalic acid and ethylene glycol, add them to the primary esterification reactor and mix them evenly, then add ethylene glycol antimony, an esterification catalyst, to the primary esterification reactor and stir evenly, wherein the amount of catalyst added is 1.6×10 of the amount of terephthalic acid. -4 times;

[0041] S2. After the reaction is complete, the material is passed into a secondary esterification reactor, and the temperature in the secondary esterification reactor is raised to 260 ° C to allow the raw materials to undergo sufficient esterification reaction;

[0042] S3. After the esterification is completed, the material is passed into a primary polymerization kettle, and then a catalyst (ethylene glycol antimony) is added to the primary polymerization kettle; wherein the amount of the catalyst added is 1.5×10 -4 times; control the reaction temperature of the first-stage polymerization reactor to 270°C;

[0043] S4. After the reaction is complete in the first polymerization reactor, the material is passed into the second polymerization reactor, and the reaction temperature of the second polymerization reactor is controlled to be 270 ° C;

[0044] S5. After the reaction in the secondary polymerization kettle is completed, the material is passed into the tertiary polymerization kettle. After the reaction is completed, a stabilizer is added (the addition time is 30 minutes before the end of the reaction). The amount of stabilizer added is 1.6×10 of the amount of terephthalic acid. -4 times;

[0045] At the same time, the reaction temperature is controlled to be 275°C; polyethylene terephthalate with high polymerization degree is prepared;

[0046] Step 2

[0047] The prepared high-polymerization polyethylene terephthalate is transported to the spinning process, and the transport and parking temperature is maintained at 265±5℃, and the transport and parking time is as short as possible. The spinning process is divided into the pre-spinning process and the post-spinning process, specifically:

[0048] S1. Pre-spinning: adopt multi-roller stretching system; control the screw temperature of the screw extruder to 295±5℃, the spinning box temperature: 290±5℃; use ring blowing during cooling and curing, the temperature is 25±2℃, the wind speed is 0.5~0.6m / s; the total stretching multiple during the stretching process is 4.3 times;

[0049] S2. Post-spinning includes stretching, heat treatment and fiber curling processes; the stretching process is wet heat stretching and secondary stretching;

[0050] The parameters that need to be controlled in the post-spinning process are: primary stretching temperature 80°C, primary stretching ratio ≥90%; secondary stretching temperature 180°C, water vapor pressure 1.0±0.13MPa; feeding speed 40±5m / min, yarn output speed 150±10m / min; total stretching ratio 4.0±0.2 times; the temperature of the step-by-step drawing and tension heat setting process is 120°C; the maximum water vapor pressure is 1.13MPa, and the heat setting time is controlled at 40±5s; the fiber curling temperature is controlled at 85°C.

[0051] Experimental verification: The polyester fiber prepared in Example 1 was extracted to calculate the surface oligomer content.

[0052] The specific test methods are as follows:

[0053] Accurately weigh about 10g of PET staple fibers (linear density of 1.33dtex, length of 38mm), wrap them with filter paper and place them in a Soxhlet extractor. First, quickly rinse them with trichloroethylene at room temperature 2 to 3 times to remove the oil agent, and treat the eluent separately. Then adjust the oil bath heating temperature to 120℃, stabilize the condensed liquid droplet flow rate to 1 to 2 drops / s, and extract with trichloroethylene for 10h. Wash the extracted PET staple fibers with trichloroethylene 2 to 3 times, pour them into a flask and heat and distill them. Transfer the obtained oligomer concentrate to a beaker; wash them with trichloroethylene 2 to 3 times, and pour the washing liquid into a beaker; heat and evaporate them, place them in a constant temperature drying oven at 87℃ and dry them for 1h, take them out and place them in a dryer to cool them to room temperature and weigh them (accurate to 0.1mg); repeat the operation until the difference between the two masses is less than 0.3mg, which is considered to be completely evaporated. Trichloroethylene extracted PET staple fibers (Tr-PETS) are dried in a fume hood for use.

[0054] The calculation of surface oligomer content is shown in (Formula 1):

[0055]

[0056] Wherein: Y is the surface oligomer content, %; m1 is the mass of the beaker and surface oligomers after extraction, g; m0 is the mass of the flask before extraction, g; m is the mass of the PET staple fiber sample, g.

[0057] After testing and calculation (three repeated tests), the average total oligomer content of the polyester fiber prepared in Example 1 is 0.48%. The surface morphology of the polyester fiber prepared in Example 1 was observed by scanning electron microscopy. Figure 1 .Depend on Figure 1 It can be seen that the polyester fiber prepared in Example 1 is uniform in thickness and has less surface oligomers.

[0058] The following example (single factor test) was set up on the basis of Example 1, and the specific setting method is shown in Table 1. The total oligomer content was tested in the same manner as Example 1, and the results are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] Note: The settings of the examples and comparative examples in Table 1 are all single factor experiments. Except for the above parameters set according to Table 1, the remaining steps and parameters are the same as those in Example 1. "Total surface oligomer content" refers to the sum of the contents of all surface polymers within a degree of polymerization of 1-20, including linear oligomers and cyclic oligomers.

[0063] The surface morphology of the polyester fiber prepared in Comparative Example 1-2 was observed by scanning electron microscope. Figure 2-3 .Depend on Figure 2-3 It can be seen that the oligomer particles attached to the surface of polyester fibers are Figure 1 The content should be increased, and the most obvious increase is Figure 2 .

[0064] In order to investigate the influence of the process conditions in the spinning stage on the oligomer content on the surface of the polyester fiber, the present invention sets Examples 9-11 and Comparative Examples 4-6 (three repeated samples are set for each example). Specific parameter settings are shown in Table 2.

[0065] Table 2

[0066]

[0067] Note: The settings of the examples and comparative examples in Table 2 are all single factor experiments. Except for the above parameters set according to Table 1, the remaining steps and parameters are the same as those in Example 1. "Total surface oligomer content" refers to the sum of the contents of all surface polymers within a degree of polymerization of 1-20, including linear oligomers and cyclic oligomers.

[0068] In Comparative Example 4, the stretching ratio in the pre-spinning stage is increased on the basis of Example 1, and the total content of the prepared surface oligomers is increased compared with that in Example 1. The possible reason is that the excessive stretching ratio causes a certain degree of mechanical damage on the surface of the polyester fiber, and a part of the internal oligomers migrate to the surface during the subsequent treatment process.

[0069] Comparative Example 5 increases both the primary stretching temperature and the secondary stretching temperature in the post-spinning stage on the basis of Example 1, and the surface oligomer content also increases. The possible reason is that the increase in temperature at this stage causes part of the internal oligomers to migrate to the surface, resulting in an increase in the surface oligomer content.

[0070] Comparative Example 6 increases the temperature of the step-by-step drawing and tense heat setting processes in the post-spinning stage on the basis of Example 1. It is found that the surface oligomer content of the polyester fiber prepared in Comparative Example 1 also increases accordingly. It is speculated that the reason may be similar to that of Comparative Example 5.

[0071] In summary, the content of surface oligomers depends on the synergistic effect of each process in the reaction stage and the spinning stage. The present invention designs a method for preparing polyester fibers with low surface oligomer content by studying the influence of each process stage on the formation of oligomers, thereby achieving the purpose of reducing the content of surface oligomers in polyester fibers.

[0072] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing polyester fiber with low content of surface oligomers, characterized in that: Using terephthalic acid and excess ethylene glycol as raw materials, esterification reaction is performed to generate dihydroxyethyl terephthalate, and then polycondensation reaction is performed under the action of a catalyst to obtain high-polymerization degree polyethylene terephthalate; and then the polyethylene terephthalate is spun and post-treated to prepare polyester fiber; Wherein, in the esterification reaction stage, the molar ratio of ethylene glycol to terephthalic acid is EG / PTA=1.05-1.10, and in the final polycondensation reaction stage, the reaction temperature is 270-280°C; The spinning process includes a pre-spinning process stage and a post-spinning process stage; the stretching process of the pre-spinning process and the post-spinning process both adopts multi-roller stretching; wherein the total stretching multiple of the pre-spinning stretching process is 4.3±0.2 times; The total stretching ratio of the stretching process in the post-spinning stage is 4.0±0.2 times, and the primary stretching ratio is ≥90%; the primary stretching temperature is 80±5°C; the secondary stretching temperature is 180±5°C; the water vapor pressure is 1.0±0.13MPa; the temperature of the step-by-step drawing and tense heat setting process in the post-spinning process stage is 70°C to 185°C; the maximum water vapor pressure is 1.13MPa, and the heat setting time is controlled at 40±5s.

2. The method for preparing polyester fiber with low surface oligomer content according to claim 1, characterized in that: In the esterification reaction stage, the molar ratio of ethylene glycol to terephthalic acid is EG / PTA=1.06, and in the final polycondensation reaction stage, the reaction temperature is 275°C.

3. The method for preparing polyester fiber with low surface oligomer content according to claim 1, characterized in that: The final polycondensation reaction stage also includes the step of adding a stabilizer; the stabilizer is a phosphate stabilizer; the amount of the stabilizer added is 1.0 to 1.8×10 of the amount of terephthalic acid. -4 times.

4. The method for preparing polyester fiber with low surface oligomer content according to claim 1, characterized in that: During the cooling and solidification in the pre-spinning process stage, ring blowing or side blowing is used, with a temperature of 25±2° C. and a wind speed of 0.5-0.6 m / s.

5. The method for preparing polyester fiber with low surface oligomer content according to claim 1, characterized in that: The catalyst is antimony glycol or SbAc3; the amount of catalyst added is 1.8 to 2.4×10 -4 mol / mol terephthalic acid.

6. The method for preparing polyester fiber with low surface oligomer content according to claim 1, characterized in that: When the polyethylene terephthalate is transported before spinning, the transport and storage temperatures are maintained below 280°C.

7. The method for preparing polyester fiber with low surface oligomer content according to claim 1, characterized in that: The esterification reaction stage also includes the step of adding an esterification catalyst; the esterification catalyst is organic antimony.

8. A polyester fiber with a low content of surface oligomers prepared by the preparation method according to any one of claims 1 to 7.

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