Preparation method of polytetrafluoroethylene sewing thread

Abstract

The invention relates to the technical field of polytetrafluoroethylene, and discloses a preparation method of a polytetrafluoroethylene sewing thread, which comprises the following steps: S1, mixing polytetrafluoroethylene emulsion with a boosting agent to obtain a mixture; s2, carrying out curing treatment on the mixture; s3, the cured mixture is preformed, and a blank is obtained; s4, putting the blank into an extrusion system, and extruding a columnar material; s5, calendering the columnar material by using a double-roller calender to obtain a flaky material; s6, the sheet-shaped materials are wound and cut into strip-shaped materials; s7, twisting the strip-shaped material into a single-strand or multi-strand material; s8, extracting and removing the boosting agent; and S9, the materials are subjected to average tension treatment. According to the preparation method provided by the invention, the temperature resistance, the strength and the toughness of the sewing thread can be improved, the overall mechanical property of the sewing thread is improved, the thread breaking condition on high-speed sewing equipment is reduced, the overall durability and reliability are ensured, and the production efficiency and the quality are further improved.

Description

Technical Field

[0001] The invention relates to the technical field of polytetrafluoroethylene, in particular to a preparation method of polytetrafluoroethylene sewing thread. Background Art

[0002] As a high-performance engineering plastic, polytetrafluoroethylene (PTFE) has been widely used in many industries due to its outstanding chemical stability, excellent mechanical properties and good electrical insulation properties. In particular, due to its excellent heat resistance and cold resistance, PTFE is often used to make sewing threads that can work under extreme temperature conditions. However, despite these advantages, traditional PTFE sewing threads still have some shortcomings, which limits their application in certain high-intensity working environments.

[0003] During actual use, especially when subjected to external impact or under complex working conditions, traditional PTFE sewing thread is prone to breakage, affecting its service life. Due to the limitations of the material itself, the strength of ordinary PTFE sewing thread cannot meet the requirements of high-strength sewing, especially in application scenarios that need to withstand large tensile forces. The tensile performance of traditional PTFE sewing thread is poor, which leads to easy breakage when using high-speed sewing equipment. Secondly, although the existing PTFE can have a certain high temperature resistance, under some specific conditions of use, especially when it needs to be used in a high temperature environment for a long time, the high temperature resistance of PTFE in the prior art is relatively general. These problems limit the performance of polytetrafluoroethylene sewing thread in certain high-demand applications, especially in situations where high strength and good toughness are required. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a method for preparing polytetrafluoroethylene sewing thread.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a polytetrafluoroethylene sewing thread comprises the following steps: S1: mixing a polytetrafluoroethylene emulsion with a propellant to obtain a mixture; S2: performing a aging treatment on the mixture; S3: pouring the aging mixture into a mold for preforming treatment to obtain a blank; S4: placing the preformed blank into an extrusion system to extrude a columnar material; S5: using a double-roller calender to calender the extruded columnar material to obtain a sheet material; S6: rolling the sheet material, and cutting the rolled material into strip materials by a slitting machine; S7: twisting a plurality of strip materials into a single strand or multiple strands of material by a twisting machine; S8: extracting and removing the propellant in the single strand or multiple strands of material; S9: performing an average tension treatment on the extracted material, finally obtaining the polytetrafluoroethylene sewing thread, and rolling and plastic sealing.

[0007] As a preferred technical solution of the present invention, before performing step S1, the polytetrafluoroethylene emulsion is pretreated, wherein the pretreatment includes: A1: refrigerating the polytetrafluoroethylene emulsion in a low-temperature environment; A2: performing directional freezing on the polytetrafluoroethylene emulsion that has undergone preliminary refrigeration treatment; A3: slowly heating up to thaw the material; A4: repeating steps A2-A3 3-5 times.

[0008] As a preferred technical solution of the present invention, in step A3, the thawing process is divided into three stages: an initial slow heating stage: a stirring speed of ≤10rpm, stirring for 5 to 10s every 5 to 10min; an accelerated heating stage: a stirring speed of 10 to 20rpm, stirring for 10-20s every 3 to 5min; and a late natural heating stage: a stirring speed of ≤30rpm.

[0009] As a preferred technical solution of the present invention, in step S1: the weight parts of the polytetrafluoroethylene emulsion and the propellant are 80-100 and 10-20 respectively; the mixing speed is 20-30 r / min; and the mixing time is 10-30 min.

[0010] As a preferred technical solution of the present invention, in the step S2, the aging treatment includes: B1: allowing the mixed and stirred mixture to stand for the first time, the standing temperature is 22 to 30°C, the standing time is 2 to 5 hours, and periodic temperature fluctuations are set during this period; B2: allowing the mixture to stand again for 18 to 32 hours, performing aging treatment at a temperature of 25 to 30°C, and applying low-intensity ultrasound during this period, with an interval of 5 to 6 hours each time, and each time lasting 5 to 10 minutes.

[0011] As a preferred technical solution of the present invention, the extrusion system in step S4 includes: a feeding hopper: the temperature is 20-30°C; a twin-screw extruder: divided into several temperature zones, the overall temperature is 30-80°C, the screw speed is 20-30r / min, and the pushing pressure is 1-2MPa; a cooling zone: the temperature is 40-60°C.

[0012] As a preferred technical solution of the present invention, in step S5: the roller temperature of the double-roller calender is 60-80°C; the calendering speed is 2-10m / min; the roller spacing is reduced by 0.05-0.1mm each time; and the thickness of the sheet material is 0.05-0.2mm.

[0013] As a preferred technical solution of the present invention, in step S6, the width of the strip material is 8-12 mm.

[0014] As a preferred technical solution of the present invention, in the step S7, the twisting process includes: pre-tension adjustment: the pre-tension is 0.5-1.5N, and the control time is 5-10s; gradual twisting: using a single yarn machine to twist two strip materials into a double-strand material, twisting the double-strand material with a single strip material to form a three-strand material, repeating the second twisting process, and twisting the multiple strands of silk with the single silk material in turn; heat setting treatment: the heating temperature is 60-80°C, and the heat treatment time is 30-60min.

[0015] As a preferred technical solution of the present invention, the step S8 includes: introducing vibration using an ultrasonic vibration device during the extraction process, the vibration frequency of which is 50 to 100 Hz; and low-temperature drying treatment, the drying temperature of which is 40 to 60°C.

[0016] The present invention has the following beneficial effects:

[0017] 1. Improve structural strength: The preparation method proposed in this application ensures that the materials are more closely and evenly bonded through processes such as pretreatment of polytetrafluoroethylene emulsion, special aging treatment, and gradual twisting, thereby reducing stress concentration points and significantly improving the tensile strength of the sewing thread. Especially in the case of high stretch ratio, it can effectively prevent the occurrence of breakage, improve the overall mechanical properties, and make the sewing thread more durable under complex working conditions, and suitable for high-strength sewing requirements;

[0018] 2. Improved temperature resistance: This application optimizes the preparation process to help the molecular chains to rearrange more tightly, thereby strengthening the internal network of the material and reducing internal stress, which significantly improves the temperature resistance and thermal stability of the sewing thread, allowing it to remain stable over a wider temperature range and also increases the service life of the sewing thread at high temperatures;

[0019] 3. Improve toughness: This application has made innovations and improvements in the preparation process of sewing thread, which has improved the ductility and toughness of the sewing thread, ensured its fatigue resistance during high-intensity applications, reduced thread breakage on high-speed sewing equipment, improved overall durability and reliability, and thus improved production efficiency and quality;

[0020] 4. Broad application prospects: The sewing thread prepared in the present application has broader application prospects in industrial production, especially in situations where high strength and good toughness are required. By comprehensively improving the temperature resistance, structural strength and toughness, the sewing thread of the present application can meet various harsh working environment requirements and is suitable for a variety of application scenarios, especially for high-speed sewing machines, thereby improving the product's production efficiency and market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The present invention provides a flow chart of a method for preparing polytetrafluoroethylene sewing thread. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0023] Reference Figure 1 , a method for preparing polytetrafluoroethylene sewing thread, comprising the following steps:

[0024] S1: mixing a polytetrafluoroethylene emulsion with a propellant to obtain a mixture;

[0025] Before performing step S1, the polytetrafluoroethylene emulsion is pretreated, wherein the pretreatment includes:

[0026] A1: Initial refrigeration: refrigerate the polytetrafluoroethylene dispersion resin in a low temperature environment, where the ambient temperature is 10-20°C and the refrigeration time is 20-30 hours to ensure the consistency and purity of the raw materials;

[0027] A2: Directional freezing, the dispersed resin that has undergone preliminary refrigeration treatment is loaded into a mold with a directional cooling channel, such as using liquid nitrogen injection or other efficient refrigeration technology to ensure uniform cooling along a specific direction, so that the resin can be uniformly cooled along a specific direction. The cooling temperature is -10 to -40°C, and the maintenance time is 1 to 3 hours. This process can induce the formation of an orderly arranged microcrystalline structure at the molecular scale. These microcrystals will become the basis for enhancing fiber strength in subsequent processing;

[0028] A3: Thawing and rearrangement. After directional freezing, the temperature is slowly raised to gradually thaw the raw materials. During this process, due to the existence of the previously formed microcrystalline structure, when the temperature rises, the molecular chains will have more opportunities to rearrange into a more compact and orderly state, which helps to improve the mechanical properties of the final product.

[0029] Furthermore, during the freezing and thawing process, the temperature change is controlled by a gradient, where the temperature change rate is 1 to 5°C / min. The slower and controlled cooling process helps the molecular chains to gradually relax and arrange in a specific direction, forming a more regular and stable microcrystalline structure, preventing the generation of large thermal stress inside the material, which is crucial to improving the mechanical properties of the finished sewing thread.

[0030] Furthermore, during the thawing process, a stirring device is used to slowly stir the raw materials, specifically, the initial slow heating stage: during this period, since the temperature is still very low and the material is relatively fragile, the stirring speed is ≤10rpm, and short intermittent stirring is performed, stirring for 5 to 10 seconds every 5 to 10 minutes; the mid-term accelerated heating stage: as the temperature rises, the material gradually softens. At this time, the stirring speed is increased to 10 to 20rpm, but the intermittent operation mode is still maintained, stirring for 10-20 seconds every 3 to 5 minutes; the late natural heating stage: when the temperature approaches or reaches 0°C, the material becomes softer. At this time, the stirring frequency and duration can be adjusted according to actual conditions, but the stirring speed is ≤30rpm to avoid excessive disturbance.

[0031] A4: Repeat steps A2-A3 3-5 times in multiple cycles. Each cycle will prompt more molecular chains to participate in the orderly arrangement, thereby gradually building a stronger internal network. The increase in the crystallinity of the material will help the finished sewing thread have higher tensile strength, better toughness and temperature resistance.

[0032] Furthermore, in step S1, the weight proportions of the polytetrafluoroethylene emulsion and the propellant are 80-100 and 10-20 respectively; the polytetrafluoroethylene emulsion and the propellant are placed in a closed mixer, the stirring speed is 20-30 r / min, the stirring time is 10-30 min, and the mixing temperature is 20-30° C. Furthermore, the propellant is at least one of vegetable oil, fatty acid amide and natural wax. The propellant can improve the fluidity of the PTFE emulsion, help prevent the material from agglomerating or forming agglomerates during processing, and ensure uniform dispersion. Moreover, these propellants have good renewability and biodegradability, which conforms to the concept of modern green manufacturing.

[0033] Furthermore, the mixing process of the polytetrafluoroethylene emulsion and the propellant is located in a dynamic vacuum environment, establishing a closed and evacuable mixing system to maintain the internal pressure below 10 -2 mbar, and equipped with an effective exhaust device to continuously discharge possible gases. Under vacuum conditions, moisture and other impurities in the air can be effectively removed to prevent them from interfering with the mixing process. In addition, the vacuum environment also helps to reduce the volatilization loss of the propellant and can alleviate the problem of local temperature rise caused by stirring to a certain extent.

[0034] S2: The mixture is subjected to a aging treatment, specifically comprising:

[0035] B1: The mixed and stirred mixture is allowed to stand for the first time at a temperature of 22-30°C for 2-5 hours. During this period, a periodic temperature fluctuation is set, for example, the temperature is raised from 25°C to 30°C, and then dropped from 30°C to 25°C, with each cycle lasting 1-2 hours. This dynamic temperature control helps to gradually release internal stress and reduce possible local stress concentration points. It can also promote a more orderly arrangement of molecular chains and improve the mechanical properties of the final product.

[0036] B2: Let it stand for 18 to 32 hours again and perform aging treatment at a temperature of 25 to 30°C. During this process, apply low-intensity ultrasound regularly, with an interval of 5 to 6 hours each time and a duration of 5 to 10 minutes each time. Ultrasonic waves can promote further relaxation and rearrangement of molecular chains, enhance the interaction between the propellant and PTFE particles, and improve uniformity and stability.

[0037] Furthermore, during the aging process, the mixture is placed in a sealed container, and an inert gas such as nitrogen or argon is introduced into the sealed container to maintain a slightly positive pressure state. The inert gas atmosphere can effectively isolate oxygen and other potential pollutants, prevent material oxidation or unnecessary chemical reactions, and ensure the consistency and long-term stability of product quality.

[0038] S3: Pour the matured mixture into a mold for preforming. The single pressure of the preforming is 5-20kg / cm 2 , the compression ratio is 50-150, and the blank is obtained. The preforming step can effectively remove the air bubbles in the material to prevent the formation of cavities or bubbles in the subsequent processing, which will affect the quality of the finished product. Secondly, it helps to increase the density of the material, so that the components are in closer contact, thereby ensuring the uniformity during subsequent processing. At the same time, preforming can initially shape the material into a shape suitable for entering the extruder, which is convenient for continuous processing;

[0039] S4: placing the preformed billet into a twin-screw extruder system to extrude a columnar material, wherein the extrusion system comprises:

[0040] The feeding hopper is equipped with a screw propeller to ensure that the material enters the extruder continuously and evenly. At the same time, a temperature control system is set to maintain the temperature of the feeding area at 20-30°C. Keeping the material at a low temperature can prevent the material from softening prematurely and maintain its good fluidity and plasticity;

[0041] The twin-screw extruder is equipped with heating elements and temperature control systems, including a preheating section at 30-40°C. Slight preheating helps to initially soften the material, making it easier to pass through the extruder, but does not cause premature plasticization of the material; a degassing section at 50-70°C. This temperature is enough to soften the material slightly and promote the escape of air from the material, but is not enough to cause significant plasticization or degradation of the PTFE, thereby ensuring the tightness of the extruded material and preventing cracks or holes; a compaction section at 60-80°C. This section helps to further compact the material, but still remains below the critical point where PTFE begins to significantly plasticize. This step is intended to ensure that the material density increases without destroying its structure;

[0042] Cooling zone: The temperature is 40-60°C. The lower temperature helps to fix the shape and ensure that the material is compact enough when leaving the extruder, while avoiding deformation or hardening of the material due to overheating.

[0043] Furthermore, the screw speed of the extruder is 20 to 30 r / min, and the pushing pressure is 1 to 2 MPa.

[0044] Such a design not only helps to reduce internal stress, but also maintains the flexibility of the PTFE molecular chain, thereby improving the overall quality and processing performance of the product.

[0045] S5: calendering the columnar material after extrusion, specifically, using a double-roller calender, the roller temperature is 60-80°C, the calendering speed is 2-10m / min, it is worth noting that during the calendering process, the roller spacing is gradually adjusted: starting from a wider spacing according to the amount of material, and gradually reducing to the target thickness, each adjustment range should not be too large, usually reducing 0.05-0.1mm each time to avoid excessive compression at one time causing internal stress concentration of the material. Such gradual adjustment can ensure uniform extension of the material, reduce internal stress accumulation, and prevent material rupture or cracks. After calendering, a sheet material is obtained, the thickness of the material is 0.05-0.2mm, and the material after calendering is naturally cooled to room temperature;

[0046] S6: Roll up the sheet material, and divide the rolled material into strip materials with a width of 8-12 mm through a slitting machine;

[0047] S7: twisting a plurality of strip materials into a single strand or multiple strands of material through a twisting machine, specifically, comprising:

[0048] Pre-tension adjustment: Apply appropriate pre-tension before twisting to ensure that the filament material maintains appropriate tightness during the twisting process. Specifically, use a tension controller to set the tension parameter range to 0.5-1.5N and the control time to 5-10s to ensure that the pre-tension is applied for a sufficient time to stabilize the filament material.

[0049] Step-by-step twisting: First, use a single yarn machine to twist two strip materials into a double-strand material. The twisting direction is Z or S, the twisting speed is 100-400r / min, and the twist is 100-300 twists / m. Then use a re-twisting machine to twist the double-strand material with a single strip material to form a three-strand material. The twisting direction is opposite to the first twisting direction. If the first time is in the Z direction, the second time is in the S direction to increase the structural stability. The twisting speed is 100-350r / min, the twist is 80-200 twists / m, and the second twisting process is repeated. The multi-strand yarn and the single silk material are re-twisted in turn, and the direction of each re-twisting is opposite to the previous re-twisting direction. The equipment parameters during twisting are consistent with the parameters during the second twisting.

[0050] Through this twisting design, each time a new filamentary material is added and the twist direction is changed, each step can be fully wound and stress distributed, forming a tighter and more stable structure, reducing internal defects and stress concentration points, and helping to improve the elastic recovery ability of the sewing thread, so that it can return to its original shape faster after being stressed, maintain a good shape, and improve the structural strength of the sewing thread.

[0051] S8: Extract and remove the booster in the material. Specifically, use two extraction pools in series. The first pool is used for preliminary extraction, and the second pool is used for deep extraction to ensure that the booster is completely removed. The dual-pool design can significantly improve the extraction efficiency and thoroughness. The extractant is acetone, ethanol, etc. The residence time is 1-2h. During the extraction process, an ultrasonic vibration device is used to introduce slight vibration with a vibration frequency of 50 to 100 Hz, which can promote the contact between the extractant and the material and improve the extraction efficiency.

[0052] S9: The extracted material is subjected to average tension treatment and rolled up for plastic sealing. Specifically, a stretching machine is used to stretch it slowly and evenly, with the stretching length increasing by 2% to 4% per minute to ensure that the material is evenly deformed without damage. Each stage of stretching is maintained for 30 to 60 seconds to avoid excessive stress concentration. The appropriate stretching ratio is set according to the material properties and application requirements, and the overall stretching ratio shall not exceed 10% of the original length.

[0053] Embodiment 1

[0054] S1: Weigh 850g of polytetrafluoroethylene emulsion and 150g of vegetable oil, and pretreat the polytetrafluoroethylene emulsion:

[0055] Refrigerate the emulsion at 15°C for 25 hours;

[0056] The emulsion was subjected to directional freezing treatment, with a cooling temperature of -25°C, a holding time of 2h, and a cooling rate of 3°C / min;

[0057] The emulsion was thawed. In the initial slow heating stage, the temperature change rate was 1°C / min, the stirring speed was 8 rpm, and the stirring was 8 s every 8 min. In the mid-term accelerated heating stage, the temperature change rate was 2°C / min, the stirring speed was 15 rpm, and the stirring was 15 s every 4 min. In the late natural heating stage, the temperature change rate was 1°C / min, and the stirring speed was 25 rpm.

[0058] Repeat this freeze-thaw process 4 times;

[0059] The pretreated polytetrafluoroethylene emulsion and vegetable oil are placed in a closed container, stirred at a speed of 25 r / min, a stirring time of 20 min, and a mixing temperature of 25° C. to obtain a mixture;

[0060] S2: The mixture was initially allowed to stand for 4 hours, during which the temperature was increased from 25°C to 30°C and then decreased from 30°C to 25°C, with each cycle lasting 1 hour, and then allowed to stand again for aging, with the standing temperature being 27°C and the standing time being 24 hours. During this process, low-intensity ultrasound was applied, with each interval of 6 hours and each duration of 8 minutes;

[0061] S3: Preform the matured mixture with a single pressure of 10kg / cm 2 , compression ratio is 100;

[0062] S4: put the preformed material into the extrusion system for extrusion, the feed hopper temperature is 25°C, the preheating section of the twin-screw extruder is 35°C, the degassing section is 60°C, the compacting section is 70°C, the cooling zone is 50°C, the screw speed is 25r / min, and the pushing pressure is 1.5MPa;

[0063] S5: The extruded material is calendered, the roller temperature is 70°C, the calendering speed is 6m / min, and the spacing is gradually adjusted: each time it is reduced by 0.08mm, and the thickness of the sheet material finally obtained is 0.1mm;

[0064] S6: Roll up the sheet material, and divide the rolled material into strip materials with a width of 10 mm through a slitting machine;

[0065] S7: Put 5 strips of material into the twisting machine, the pre-tension parameter is 1N, the control time is 8s, and the twisting is performed in a step-by-step twisting manner. The twisting direction is the Z direction, the twisting speed is 300r / min, and the twist is 200 twists / m to obtain a single strand of material;

[0066] S8: placing the single strand of material into an extraction cell to extract the booster therein, the extractant is acetone, the residence time is 1.5 hours, and the frequency of ultrasonic vibration is 75 Hz;

[0067] S9: The extracted single strand material is stretched at a stretching rate of 2% increase in stretching length per minute, each stage is held for 45 seconds, and the total stretching ratio is 1.1 times, and finally polytetrafluoroethylene sewing thread is obtained.

[0068] The performance of the polytetrafluoroethylene sewing thread was tested, wherein the long-term high temperature resistance was 220.7°C, the short-term high temperature resistance was 260.4°C, the tensile strength was 305.2MPa±18.5MPa, and the elongation at break was 26.3%±4.2%.

[0069] Embodiment 2

[0070] The difference from the first embodiment is that:

[0071] S1: Weigh 850g of polytetrafluoroethylene emulsion and 150g of vegetable oil, and pretreat the polytetrafluoroethylene emulsion:

[0072] Refrigerate the emulsion at 10°C for 30 hours;

[0073] The emulsion was subjected to directional freezing treatment, with a cooling temperature of -40°C, a holding time of 3h, and a cooling rate of 1°C / min;

[0074] The emulsion was thawed. In the initial slow heating stage, the temperature change rate was 1°C / min, the stirring speed was 5 rpm, and the stirring was 5 s every 5 min. In the mid-term accelerated heating stage, the temperature change rate was 2°C / min, the stirring speed was 10 rpm, and the stirring was 10 s every 5 min. In the late natural heating stage, the temperature change rate was 1°C / min, and the stirring speed was 20 rpm.

[0075] Repeat this freeze-thaw process 5 times;

[0076] The pretreated polytetrafluoroethylene emulsion and vegetable oil are placed in a closed container, stirred at a speed of 25 r / min, a stirring time of 20 min, and a mixing temperature of 22° C. to obtain a mixture;

[0077] The remaining steps are the same as those in the first embodiment.

[0078] The performance of the polytetrafluoroethylene sewing thread was tested, wherein the long-term high temperature resistance was 223.1°C, the short-term high temperature resistance was 262.8°C, the tensile strength was 310.5MPa±17.8MPa, and the elongation at break was 27.5%±4.0%.

[0079] Embodiment 3

[0080] The difference from the first embodiment is that:

[0081] S2: The mixture was initially allowed to stand for 5 hours, during which the temperature increased from 22°C to 30°C and then decreased from 30°C to 22°C, with each cycle lasting 1 hour. The mixture was then allowed to stand for aging again, with a standing temperature of 30°C and a standing time of 24 hours. Low-intensity ultrasound was applied during the process, with each interval of 5 hours and each duration of 10 minutes.

[0082] The remaining steps are the same as those in the first embodiment.

[0083] The performance of the polytetrafluoroethylene sewing thread was tested, wherein the long-term high temperature resistance was 221.8°C, the short-term high temperature resistance was 261.2°C, the tensile strength was 307.6MPa±17.9MPa, and the elongation at break was 26.7%±4.3%.

[0084] Embodiment 4

[0085] The difference from the first embodiment is that:

[0086] S8: Put the single strand material into an extraction cell to extract the booster therein, the extractant is acetone, the residence time is 2 hours, and the frequency of ultrasonic vibration is 100 hours.

[0087] The remaining steps are the same as those in the first embodiment.

[0088] The performance of the polytetrafluoroethylene sewing thread was tested, wherein the long-term high temperature resistance was 220.9°C, the short-term high temperature resistance was 260.6°C, the tensile strength was 306.5MPa±18.2MPa, and the elongation at break was 26.4%±4.1%.

[0089] It is briefly explained that in the above embodiments, the temperature resistance is reflected by long-term high temperature resistance and short-term high temperature resistance. The long-term high temperature resistance refers to GB / T 7141-2008 "Test method for long-term heat aging of plastics", and the short-term high temperature resistance refers to GB / T 1634.2-2004 "Determination of load deformation temperature of plastics Part 2: Plastics, hard rubber and reinforced thermosetting plastics", the tensile strength refers to GB / T 528-2009: "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", and the elongation at break refers to GB / T 528-2009: "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0090] In summary, the present application optimizes and improves the preparation method of polytetrafluoroethylene sewing thread. When the parameters of the prepared polytetrafluoroethylene sewing thread are measured, the long-term high temperature resistance temperature is >220°C, the short-term high temperature resistance temperature is >260°C, the tensile strength is >250MPa, and the elongation at break is >20%. This significantly improves the temperature resistance, toughness and structural strength of the sewing thread, reduces the fatigue of the material, and reduces the risk of thread breakage and wear, so that it can be used on high-speed sewing machines to improve sewing efficiency. The prepared sewing thread complies with the concept of environmental protection and has a wider application prospect in industrial production.

[0091] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing polytetrafluoroethylene sewing thread, characterized in that: The following steps are involved: S1: mixing a polytetrafluoroethylene emulsion with a propellant to obtain a mixture; S2: aging the mixture; S3: pouring the matured mixture into a mold for preforming to obtain a blank; S4: placing the preformed blank into an extrusion system to extrude a columnar material; S5: using a double-roller calender to calender the columnar material after extrusion to obtain a sheet material; S6: Roll up the sheet material, and cut the rolled material into strip material by a slitting machine; S7: twisting a plurality of strip materials into single or multiple strands of material through a twisting machine; S8: extract and remove the propellant in the single or multiple strands of material; S9: The extracted material is subjected to average tension treatment to finally obtain polytetrafluoroethylene sewing thread, which is then rolled and plastic-sealed.

2. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: Before performing step S1, the polytetrafluoroethylene emulsion is pretreated, wherein the pretreatment includes: A1: Refrigerate the polytetrafluoroethylene emulsion in a low temperature environment; A2: Directional freezing of the polytetrafluoroethylene emulsion that has undergone preliminary refrigeration treatment; A3: Slowly increase the temperature to thaw the material; A4: Repeat steps A2-A3 3-5 times.

3. The method for preparing polytetrafluoroethylene sewing thread according to claim 2, characterized in that: In step A3, the thawing process is divided into three stages: Initial slow heating stage: stirring speed ≤ 10 rpm, stirring for 5 to 10 seconds every 5 to 10 minutes; Accelerated heating stage: stirring speed is 10-20rpm, stirring for 10-20s every 3-5min; In the later stage of natural heating, the stirring speed is ≤30rpm.

4. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: In step S1: The weight parts of polytetrafluoroethylene emulsion and propellant are 80-100 and 10-20 respectively; The mixing speed is 20-30 r / min; The mixing time is 10 to 30 minutes.

5. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: In step S2, the aging process includes: B1: The mixed and stirred mixture is allowed to stand for the first time at a temperature of 22 to 30°C for 2 to 5 hours, and periodic temperature fluctuations are set during this period; B2: Allow to stand for another 18 to 32 hours, and perform aging treatment at a temperature of 25 to 30°C. During this period, low-intensity ultrasonic waves are applied, each time at intervals of 5 to 6 hours and each time for 5 to 10 minutes.

6. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: The extrusion system in step S4 comprises: Feeding hopper: temperature is 20-30℃; Twin-screw extruder: divided into several temperature zones, the overall temperature is 30-80°C, the screw speed is 20-30r / min, and the pushing pressure is 1-2MPa; Cooling zone: temperature is 40~60℃.

7. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: In step S5: the roller temperature of the double roller calender is 60-80°C; The rolling speed is 2-10 m / min; The roller spacing is reduced by 0.05-0.1mm each time; The thickness of the sheet material is 0.05 to 0.2 mm.

8. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: In step S6, the width of the strip material is 8-12 mm.

9. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: In step S7, the twisting process includes: Pre-tension adjustment: pre-tension is 0.5-1.5N, control time is 5-10s; Step-by-step twisting: Use a single yarn machine to twist two strips of material into a double-strand material, twist the double-strand material with a single strip of material to form a three-strand material, repeat the second twisting process, and twist the multiple strands of yarn with the single yarn material in turn; Heat setting treatment: heating temperature is 60-80℃, and heat treatment time is 30-60min.

10. The method for preparing polytetrafluoroethylene sewing thread according to claim 1, characterized in that: The step S8 includes: During the extraction process, an ultrasonic vibration device is used to introduce vibration, with a vibration frequency of 50 to 100 Hz; Low temperature drying treatment, the drying temperature is 40-60℃.

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