Low-permeability polytetrafluoroethylene tubes and preparation method therefor

Abstract

The present invention belongs to the technical field of polytetrafluoroethylene tubes. Disclosed are low-permeability polytetrafluoroethylene tubes and a preparation method therefor. The preparation method for low-permeability polytetrafluoroethylene tubes in the present invention is as follows: respectively weighing a TFE / HFP copolymer, an auxiliary agent, a nucleating agent, an antioxidant and an antistatic agent in parts by weight for later use; uniformly mixing the TFE / HFP copolymer, the auxiliary agent, the nucleating agent, the antioxidant and the antistatic agent in a high-speed mixer; placing the mixture, which has been stored for a period of time, in a preforming machine and subjecting same to compression molding, so as to prepare a blank; placing the blank in an extruder and extruding same, so as to prepare a raw tube blank; and drying and pre-sintering the raw tube blank, and then performing a hot isostatic pressing treatment on the raw tube blank to obtain low-permeability polytetrafluoroethylene tubes. The polytetrafluoroethylene tubes prepared in the present invention have excellent properties such as fatigue resistance, pressure resistance and bending strength, also have relatively low permeability, and can be used in fields with strict requirements on permeability.

Description

A low-permeability polytetrafluoroethylene tube and its preparation method Technical Field

[0001] This invention belongs to the field of polytetrafluoroethylene (PTFE) pipe technology, specifically relating to a low-permeability PTFE pipe and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is a high-performance material with excellent chemical stability, temperature resistance, corrosion resistance, and low coefficient of friction, and is widely used in various high-performance products, especially in the fields of wires and cables, and fluid transportation pipelines. However, its high melt viscosity and poor flowability pose significant challenges to its processing, particularly in applications requiring high precision and tight sealing.

[0003] PTFE has a melt viscosity much higher than that of general thermoplastics, making it difficult to flow and fill molds during processing. Even at high temperatures, PTFE melt still exhibits high viscosity, making processing challenging. Due to its high melt viscosity, PTFE also has poor flowability, resulting in uneven material distribution during extrusion and molding processes, easily leading to porosity and defects. Particularly in the process of extruding PTFE dispersion resin into pipes, the high melt viscosity and poor flowability of PTFE make it difficult for the melt to fully fill the tiny pores in the mold, resulting in numerous pores or microcracks inside the finished pipe. These pores or microcracks become channels for liquid or gas permeation, leading to high permeability in PTFE pipes. This not only affects the sealing performance of the pipes but may also cause liquid or gas leaks, thus impacting product lifespan and safety, and failing to meet the requirements of fields with stringent permeability requirements.

[0004] Therefore, developing a polytetrafluoroethylene (PTFE) pipe that can meet the above-mentioned strict requirements for permeability has become one of the problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention discloses a low-permeability polytetrafluoroethylene tube and its preparation method. The present invention prepares a low-permeability, high-performance polytetrafluoroethylene tube by adopting a pre-sintering and hot isostatic pressing process.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A low-permeability polytetrafluoroethylene pipe is made from the following raw materials in parts by weight: 90-95 parts of TFE / HFP copolymer (i.e., modified polytetrafluoroethylene copolymerized from tetrafluoroethylene and hexafluoropropylene), 2-5 parts of additives, 1-3 parts of nucleating agent, 0.5-1 part of antioxidant, and 0.1-1 part of antistatic agent.

[0008] Preferably, the TFE / HFP copolymer comprises 94 parts, additives 3 parts, nucleating agent 2 parts, antioxidant 0.5 parts, and antistatic agent 0.5 parts.

[0009] Preferably, the additive is one of paraffin oil, zinc stearate, and silicone oil; the nucleating agent is one of triphenyl phosphite, talc, silica, and calcium carbonate; the antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant; and the antistatic agent is one of dioctadecyl dimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, and octadecyl trimethyl ammonium chloride.

[0010] The present invention also discloses a method for preparing the above-mentioned TFE / HFP copolymer, the specific steps of which are as follows:

[0011] S1. Prepare raw materials: Weigh TFE (tetrafluoroethylene), HFP (hexafluoropropylene), and BPO (benzoyl peroxide) according to the mass ratio.

[0012] S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 5 to 8 minutes. Then add BPO and continue stirring for 5 to 6 minutes to obtain a uniformly mixed material.

[0013] S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to heat and pressurize, and react for 4 to 6 hours at a temperature of 80~100°C and a pressure of 20~40MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC (gel permeation chromatography) or NMR (nuclear magnetic resonance). When the conversion rate reaches 85~95%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure inside the high-pressure reactor, open the high-pressure reactor and take out the reaction product.

[0014] S4. Cooling and drying: The reaction product in step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 60~70℃ for 24h to obtain the dried copolymer;

[0015] S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer.

[0016] Preferably, in step S1, the mass ratio of TFE to HFP is (90~95):(5~10); and the BPO is 0.2%~0.8% of the total mass of TFE and HFP.

[0017] Preferably, in step S1, the mass ratio of TFE to HFP is 95:5, and the BPO is 0.5% of the total mass of TFE and HFP.

[0018] Preferably, in step S5, the particle size of the polytetrafluoroethylene powder is 0.3~0.4mm.

[0019] This invention also discloses a method for preparing the above-mentioned low-permeability polytetrafluoroethylene tube, comprising the following steps:

[0020] (1) Weigh out the TFE / HFP copolymer, additives and nucleating agent, antioxidant and antistatic agent according to the weight parts for later use;

[0021] (2) After mixing the TFE / HFP copolymer, additives, nucleating agents, antioxidants and antistatic agents from step (1) in a high-speed mixer, store them at 10~15℃ for at least 24 hours.

[0022] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 5~8MPa and a compression rate of 40~50mm / min to obtain a blank;

[0023] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 40~50℃, a die temperature of 50~60℃, and an extrusion rate of 80~100mm / min to obtain a green tube blank.

[0024] (5) After drying and pre-sintering the green tube blank in step (4), the green tube blank is then subjected to hot isostatic pressing treatment to obtain a low-permeability polytetrafluoroethylene tube.

[0025] Preferably, in step (5), the drying temperature is 80~150℃ and the time is 20~24h; the pre-sintering temperature is 200~300℃ and the sintering time is 1.5~2.5h; the hot isostatic pressing treatment is 60~80MPa, the temperature is 350~400℃ and the time is 1~2 hours.

[0026] Preferably, in step (5), the drying temperature is 120°C and the time is 22h; the pre-sintering temperature is 250°C and the sintering time is 2h; the hot isostatic pressing treatment has a pressure of 70MPa, a temperature of 380°C and a time of 1.5h.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention introduces a pre-sintering and hot isostatic pressing process in the preparation of polytetrafluoroethylene tubes, which is specifically analyzed as follows:

[0029] (i) The pre-sintering disclosed in this invention is carried out at a temperature of 200~300°C. This temperature range is lower than the melting point of the TFE / HFP copolymer (usually around 327°C), but much higher than its glass transition temperature Tg (about -80~-100°C). This temperature range can promote the rearrangement of molecular chains in the material and promote the initial crystallization of the material, but will not cause the material to completely melt and form a preliminary crystalline structure. The preliminary crystallization can improve the crystallinity of the material, provide more crystal nuclei for subsequent high-temperature sintering, and promote more uniform crystallization. This can reduce internal defects and pores in the material and improve the uniformity and density of the material. Furthermore, the pre-sintering disclosed in this invention is carried out at a lower temperature, which can gradually release the internal stress of the material and avoid cracks or deformation caused by the large internal stress of the material during high-temperature sintering. At the same time, pre-sintering can reduce the thermal shock during high-temperature sintering and improve the thermal stability of the material.

[0030] (ii) The hot isostatic pressing temperature disclosed in this invention is 330~400℃. Within this temperature range, the material after the above pre-sintering can be further crystallized to form a denser structure. At the same time, the applied pressure is 60~80MPa, which can force the pores in the material to close and improve the density of the material.

[0031] In summary, this invention introduces pre-sintering and hot isostatic pressing processes. Pre-sintering is carried out at a temperature of 200-300℃, which can promote initial crystallization, gradually release internal stress, and reduce cracks and deformation during high-temperature sintering. Hot isostatic pressing is carried out at a pressure of 60-80MPa and a temperature of 330-400℃, which can significantly reduce porosity and improve the microstructure of the material, as shown in Figure 1(A). The polytetrafluoroethylene (PTFE) tubes prepared using the process provided by this invention have well-fused resin particles, good density, and good material uniformity and consistency. Furthermore, the PTFE tubes prepared using the method of this invention have good mechanical properties and low permeability (as shown in Table 1). 4) Its tensile porosity index can reach 0.12%, and its permeability is low. At the same time, its fatigue resistance (as shown in Table 1 and Figure 2) shows that after pulse testing, there are almost no longitudinal cracks at the crimping point and no leakage in the tube body, indicating good fatigue resistance. Its compressive strength (as shown in Table 2) can reach 48 MPa, which is 26.3% higher than that of the traditional preparation process (Comparative Example 1). Its bending strength (as shown in Table 3) shows that the change rate of the inner diameter after bending test is only 4%, which is 9.5% lower than that of the traditional preparation process (Comparative Example 1). It can be seen that the present invention improves the density and impermeability of the material while ensuring other mechanical properties. Attached Figure Description

[0032] Figure 1 is an electron microscope image of Embodiment 1 and Comparative Examples 1-4 of the present invention;

[0033] Figure 2 shows the anatomical diagrams of each group of samples after the pulse test of Example 1 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods; the experimental materials used are commercially available unless otherwise specified.

[0035] This invention discloses a low-permeability polytetrafluoroethylene (PTFE) pipe, which is made from raw materials comprising the following parts by weight: 90-95 parts of TFE / HFP copolymer, 2-5 parts of additives, 1-3 parts of nucleating agent, 0.5-1 part of antioxidant, and 0.1-1 part of antistatic agent; the most preferred composition is 94 parts of TFE / HFP copolymer, 3 parts of additives, 2 parts of nucleating agent, 0.5 parts of antioxidant, and 0.5 parts of antistatic agent.

[0036] The above-mentioned additives are one of paraffin oil, zinc stearate, and silicone oil; the nucleating agent is one of triphenyl phosphite, talc, silica, and calcium carbonate; the antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant; and the antistatic agent is one of bis(octadecyl)dimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0037] The preparation method of the above TFE / HFP copolymer is as follows:

[0038] S1. Prepare raw materials: Weigh TFE, HFP and BPO according to the mass ratio, wherein the mass ratio of TFE to HFP is (90~95):(5~10), and BPO is 0.2%~0.8% of the total mass of TFE and HFP; the optimal ratio is 95:5, and BPO is 0.5% of the total mass of TFE and HFP.

[0039] S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 5-8 minutes. Then add BPO and continue stirring for 5-6 minutes to obtain a uniformly mixed material.

[0040] S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to raise the temperature and pressure, and react for 4 to 6 hours at a temperature of 80~100°C and a pressure of 20~40MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC or NMR. When the conversion rate reaches 85~95%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure inside the high-pressure reactor, open the high-pressure reactor and take out the reaction product.

[0041] S4. Cooling and drying: The reaction product from step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 60~70℃ for 24h to obtain the dried copolymer.

[0042] S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer. The particle size of the obtained polytetrafluoroethylene powder is 0.3~0.4 mm.

[0043] The specific steps for preparing low-permeability polytetrafluoroethylene (PTFE) tubes using the above-mentioned raw materials are as follows:

[0044] (1) Weigh out the TFE / HFP copolymer, additives and nucleating agent, antioxidant and antistatic agent according to the weight parts for later use.

[0045] (2) After mixing the TFE / HFP copolymer, additives, nucleating agents, antioxidants and antistatic agents from step (1) in a high-speed mixer, store them at 10~15℃ for at least 24h.

[0046] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 5~8MPa and a compression rate of 40~50mm / min to obtain a blank.

[0047] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 40~50℃, a die temperature of 50~60℃, and an extrusion rate of 80~100mm / min to obtain a green tube blank.

[0048] (5) After drying the green tube blank in step (4) at 80~150℃ for 20~24h in a drying oven, place it in a sintering furnace at 200~300℃ for 1.5~2.5h for pre-sintering. After the pre-sintering is completed, after ensuring that the green tube blank is free of cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of a hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 60~80MPa, a temperature of 350~400℃ and a time of 1~2 hours. After the treatment is completed, slowly depressurize and take out the tube. That is, a low-permeability polytetrafluoroethylene tube is obtained.

[0049] The technical solution of the present invention will be further described below with reference to specific embodiments and accompanying drawings: Example 1

[0050] The preparation method of the TFE / HFP copolymer in this embodiment includes the following specific steps:

[0051] S1. Prepare raw materials: Using an electronic balance, weigh TFE and HFP according to the mass ratio (TFE:HFP=95:5); then weigh BPO according to the ratio of BPO to the total mass of TFE and HFP.

[0052] S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 6 minutes. Then add BPO and continue stirring for 5 minutes to obtain a uniformly mixed material.

[0053] S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to heat and pressurize it, and react for 5 hours at a temperature of 90°C and a pressure of 30MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC. When the conversion rate reaches 95%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure inside the high-pressure reactor, open the high-pressure reactor and take out the reaction product.

[0054] S4. Cooling and drying: The reaction product in step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 70°C for 24 hours to obtain a dried copolymer;

[0055] S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer. The particle size of the obtained polytetrafluoroethylene powder is 0.3~0.4 mm.

[0056] The specific steps for preparing low-permeability polytetrafluoroethylene pipes using the TFE / HFP copolymer prepared in this embodiment as a raw material are as follows:

[0057] (1) Weigh out the following components by weight: 94 parts TFE / HFP copolymer, 3 parts zinc stearate, 2 parts triphenyl phosphite, 0.5 parts hindered phenolic antioxidant (Irganox 1010) and 0.5 parts dioctadecyl dimethyl ammonium chloride.

[0058] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 12°C for 30 hours.

[0059] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 6 MPa and a compression rate of 45 mm / min to obtain a blank.

[0060] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 45°C, a die temperature of 55°C and an extrusion rate of 85 mm / min to obtain a green tube blank.

[0061] (5) After drying the green tube blank in step (4) at 120°C for 22 hours, place it in a sintering furnace and sinter at 250°C for 2 hours for pre-sintering. After pre-sintering, ensure that the green tube blank has no cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of a hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 70MPa, a temperature of 380°C and a time of 1.5 hours. After completion, slowly depressurize and take out the tube, that is, obtain a low-permeability polytetrafluoroethylene tube. Example 2

[0062] The preparation method of the TFE / HFP copolymer in this embodiment includes the following specific steps:

[0063] S1. Prepare raw materials: Using an electronic balance, weigh TFE and HFP according to the mass ratio (TFE:HFP=95:10); then weigh BPO according to the fact that BPO is 0.2% of the total mass of TFE and HFP.

[0064] S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 8 minutes. Then add BPO and continue stirring for 6 minutes to obtain a uniformly mixed material.

[0065] S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to heat and pressurize it, and react for 6 hours at a temperature of 100°C and a pressure of 20MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC. When the conversion rate reaches 85%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure inside the high-pressure reactor, open the high-pressure reactor and take out the reaction product.

[0066] S4. Cooling and drying: The reaction product in step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a dried copolymer;

[0067] S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer. The particle size of the obtained polytetrafluoroethylene powder is 0.3~0.4 mm.

[0068] The specific steps for preparing low-permeability polytetrafluoroethylene pipes using the TFE / HFP copolymer prepared in this embodiment as a raw material are as follows:

[0069] (1) Weigh out the following components by weight: 90 parts TFE / HFP copolymer, 2 parts paraffin oil, 1 part silica, 0.7 parts hindered phenolic antioxidant (Irganox 1010) and 0.7 parts hexadecyltrimethylammonium chloride.

[0070] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 10°C for 35 hours.

[0071] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 5 MPa and a compression rate of 40 mm / min to obtain a blank.

[0072] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 40°C, a die temperature of 50°C and an extrusion rate of 80 mm / min to obtain a green tube blank.

[0073] (5) After drying the green tube blank in step (4) at 80°C for 20 hours, place it in a sintering furnace and sinter at 200°C for 1.5 hours for pre-sintering. After pre-sintering, ensure that the sintered green tube blank has no cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of a hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 60MPa, a temperature of 350°C and a time of 1 hour. After completion, slowly depressurize and take out the tube, that is, obtain a low-permeability polytetrafluoroethylene tube. Example 3

[0074] The preparation method of the TFE / HFP copolymer in this embodiment includes the following specific steps:

[0075] S1. Prepare raw materials: Using an electronic balance, weigh TFE and HFP according to the mass ratio (TFE:HFP=95:5); then weigh BPO according to the fact that BPO is 0.8% of the total mass of TFE and HFP.

[0076] S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 8 minutes. Then add BPO and continue stirring for 6 minutes to obtain a uniformly mixed material.

[0077] S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to heat and pressurize, and react for 4 hours at a temperature of 100°C and a pressure of 40MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC. When the conversion rate reaches 90%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure inside the high-pressure reactor, open the high-pressure reactor and take out the reaction product.

[0078] S4. Cooling and drying: The reaction product in step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 70°C for 24 hours to obtain a dried copolymer;

[0079] S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer. The particle size of the obtained polytetrafluoroethylene powder is 0.3~0.4 mm.

[0080] The specific steps for preparing low-permeability polytetrafluoroethylene pipes using the TFE / HFP copolymer prepared in this embodiment as a raw material are as follows:

[0081] (1) Weigh out the following components by weight: 95 parts TFE / HFP copolymer, 5 parts paraffin oil, 1 part triphenyl phosphite, 1 part phosphite antioxidant (Irgafos 168) and 0.1 parts octadecyltrimethylammonium chloride.

[0082] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 15°C for 24 hours.

[0083] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 8 MPa and a compression rate of 50 mm / min to obtain a blank.

[0084] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 50°C, a die temperature of 60°C and an extrusion rate of 100 mm / min to obtain a green tube blank.

[0085] (5) After drying the green tube blank in step (4) at 150°C for 24 hours, place it in a sintering furnace and sinter at 300°C for 2.5 hours for pre-sintering. After pre-sintering, ensure that the sintered green tube blank has no cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of a hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 80MPa, a temperature of 380°C and a time of 2 hours. After completion, slowly depressurize and take out the tube, that is, obtain a low-permeability polytetrafluoroethylene tube. Example 4

[0086] The preparation method of the TFE / HFP copolymer in this embodiment includes the following specific steps:

[0087] S1. Prepare raw materials: Using an electronic balance, weigh TFE and HFP according to the mass ratio (TFE:HFP=90:10); then weigh BPO according to the fact that BPO is 0.6% of the total mass of TFE and HFP.

[0088] S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 8 minutes. Then add BPO and continue stirring for 6 minutes to obtain a uniformly mixed material.

[0089] S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to heat and pressurize it, and react for 5 hours at a temperature of 90°C and a pressure of 30MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC. When the conversion rate reaches 90%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure inside the high-pressure reactor, open the high-pressure reactor and take out the reaction product.

[0090] S4. Cooling and drying: The reaction product in step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 70°C for 24 hours to obtain a dried copolymer;

[0091] S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer. The particle size of the obtained polytetrafluoroethylene powder is 0.3~0.4 mm.

[0092] The specific steps for preparing low-permeability polytetrafluoroethylene pipes using the TFE / HFP copolymer prepared in this embodiment as a raw material are as follows:

[0093] (1) Weigh out the following components by weight: 92 parts TFE / HFP copolymer, 3 parts zinc stearate, 1.5 parts triphenyl phosphite, 0.8 parts phosphite antioxidant (Irgafos 168) and 0.5 parts octadecyltrimethylammonium chloride.

[0094] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 15°C for 30 hours.

[0095] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 6 MPa and a compression rate of 45 mm / min to obtain a blank.

[0096] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 45°C, a die temperature of 55°C and an extrusion rate of 90 mm / min to obtain a green tube blank.

[0097] (5) After drying the green tube blank in step (4) at 80°C for 24 hours, place it in a sintering furnace and sinter at 200°C for 2.5 hours for pre-sintering. After pre-sintering, ensure that the sintered green tube blank has no cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of a hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 60MPa, a temperature of 400°C and a time of 2 hours. After completion, slowly depressurize and take out the tube, that is, obtain a low-permeability polytetrafluoroethylene tube. Comparative Example 1

[0098] The raw materials and formulation of this comparative example are the same as those of Example 1, except that hot isostatic pressing was not used in the preparation process.

[0099] The specific steps for preparing the polytetrafluoroethylene (PTFE) tube in this comparative example are as follows:

[0100] (1) Weigh out the following components by weight: 94 parts TFE / HFP copolymer, 3 parts zinc stearate, 2 parts triphenyl phosphite, 0.5 parts hindered phenolic antioxidant (Irganox 1010) and 0.5 parts dioctadecyl dimethyl ammonium chloride.

[0101] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 12°C for 30 hours.

[0102] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 6 MPa and a compression rate of 45 mm / min to obtain a blank.

[0103] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 45°C, a die temperature of 55°C and an extrusion rate of 85 mm / min to obtain a green tube blank.

[0104] (5) After drying the green tube blank in step (4) at 120°C for 22 hours, place it in a sintering furnace and sinter at 250°C for 2 hours. Then, raise the temperature to 380°C and continue sintering for 1.5 hours to obtain a polytetrafluoroethylene tube. Comparative Example 2

[0105] The raw materials and formulation of this comparative example are the same as those of Example 1, except that the pre-sintering process was not used in the preparation process.

[0106] The specific steps for preparing the polytetrafluoroethylene (PTFE) tube in this comparative example are as follows:

[0107] (1) Weigh out the following components by weight: 94 parts TFE / HFP copolymer, 3 parts zinc stearate, 2 parts triphenyl phosphite, 0.5 parts hindered phenolic antioxidant (Irganox 1010) and 0.5 parts dioctadecyl dimethyl ammonium chloride.

[0108] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 12°C for 30 hours.

[0109] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 6 MPa and a compression rate of 45 mm / min to obtain a blank.

[0110] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 45°C, a die temperature of 55°C and an extrusion rate of 85 mm / min to obtain a green tube blank.

[0111] (5) After drying the green tube blank in step (4) at 120°C for 22 hours, ensure that the green tube blank is free of cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of the hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 70MPa, a temperature of 380°C and a time of 1.5 hours. After the treatment is completed, slowly depressurize and take out the tube. That is, a low-permeability polytetrafluoroethylene tube is obtained. Comparative Example 3

[0112] The raw materials and formulation of this comparative example are the same as those of Example 1, except that pre-sintering and hot isostatic pressing were not used in the preparation process.

[0113] (1) Weigh out the following components by weight: 94 parts TFE / HFP copolymer, 3 parts zinc stearate, 2 parts triphenyl phosphite, 0.5 parts hindered phenolic antioxidant (Irganox 1010) and 0.5 parts dioctadecyl dimethyl ammonium chloride.

[0114] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 12°C for 30 hours.

[0115] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 6 MPa and a compression rate of 45 mm / min to obtain a blank.

[0116] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 45°C, a die temperature of 55°C and an extrusion rate of 85 mm / min to obtain a green tube blank.

[0117] (5) After drying the green tube blank in step (4) at 120°C for 22 hours, place it in a sintering furnace and heat it to 380°C for 3.5 hours to obtain a polytetrafluoroethylene tube. Comparative Example 4

[0118] The difference between this comparative example and Example 1 is that it uses polytetrafluoroethylene dispersion, while the other raw materials, formulations and preparation processes are exactly the same.

[0119] The specific steps for preparing the polytetrafluoroethylene (PTFE) tube in this comparative example are as follows:

[0120] (1) Weigh out the following components by weight: 94 parts of polytetrafluoroethylene dispersion, 3 parts of zinc stearate, 2 parts of triphenyl phosphite, 0.5 parts of hindered phenolic antioxidant (Irganox 1010) and 0.5 parts of dioctadecyl dimethyl ammonium chloride.

[0121] (2) After mixing the weighed raw materials from step (1) in a high-speed mixer, store them at 12°C for 30 hours.

[0122] (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 6 MPa and a compression rate of 45 mm / min to obtain a blank.

[0123] (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 45°C, a die temperature of 55°C and an extrusion rate of 85 mm / min to obtain a green tube blank.

[0124] (5) After drying the green tube blank in step (4) at 120°C for 22 hours, place it in a sintering furnace and sinter at 250°C for 2 hours for pre-sintering. After pre-sintering, ensure that the green tube blank has no cracks, bubbles or other defects, clean the surface of the tube with a lint-free cloth and alcohol, wrap and seal the tube with a high-temperature resistant elastic rubber sleeve, and then place the packaged tube into the chamber of a hot isostatic pressing equipment. Perform hot isostatic pressing treatment at a pressure of 70MPa, a temperature of 380°C and a time of 1.5 hours. After completion, slowly depressurize and take out the tube, that is, obtain polytetrafluoroethylene tube. Performance test results:

[0125] The performance of the polytetrafluoroethylene pipes prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 was tested, as follows. 1. Electron micrograph analysis:

[0126] Figure 1 shows electron microscope images of the polytetrafluoroethylene tubes of Examples 1, 1, 2, 3, and 5 under a 1000x lens (A: Example 1, B: Comparative Example 1, C: Comparative Example 2, D: Comparative Example 3, E: Comparative Example 4). From the figures, it can be seen that: in Figure 1(A), the boundaries between resin particles are difficult to distinguish, and the pores between particles are few and small, indicating that the resin particles are well fused together, with good density and good material uniformity and consistency; in Figure 1(B), most of the resin particles are fused together, and the boundaries between particles are blurred, but the pores between particles are larger than those in Figure 1(A). The uniformity and consistency of the material in Figure 1(B) are slightly worse than those in Figure 1(A); in Figure 1(C), a small number of resin particles are well fused, but most resin particles are poorly fused, the boundaries between particles are relatively clear, and the pores between particles are relatively small compared to those in Figure (B), indicating that the crystallinity between resin particles is worse than that of the materials in Figure 1(A) and Figure 1(B); in Figure 1(D), most resin particles are poorly fused, only a small number of resin particles are fused together, and the boundaries between resin particles are relatively clear, with many and large pores between particles; in Figure 1(E), the fusion between resin particles is worse than that in Figure 1(A), and there are many pores between particles but the pore size is small. This indicates that pre-sintering at lower temperatures can promote initial crystallization of the material, increase its crystallinity, provide more nuclei for subsequent high-temperature sintering, promote more uniform crystallization, and reduce internal defects and pores. High-pressure and high-temperature hot isostatic pressing can further promote uniform crystallization, reduce grain boundary defects, and force the pores in the material to close, thereby improving the material's density and uniformity. In addition, copolymer-modified polytetrafluoroethylene has lower melt viscosity and better fluidity than unmodified polytetrafluoroethylene, which can promote better crystallization and densification. 2. Pulse test:

[0127] The polytetrafluoroethylene tubes prepared in the above five examples (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4) were subjected to pulse tests according to AS standard requirements. The number of pulses was 600,000, the working pressure was 20 MPa, and the pulse frequency was 80 times / minute. Three sample tubes were taken from each example for testing. The test results are shown in Table 1 below.

[0128] Table 1

[0129]

[0130] The samples from each group after the above tests were dissected, and the images of each group after dissection are shown in Figure 2 (A: Example 1, B: Comparative Example 1, C: Comparative Example 2, D: Comparative Example 3, E: Comparative Example 4). It can be seen from the figures that: in Figure 2(A), after the pulse test, there are almost no wrinkles at the crimping point; in Figures 2(B), 2(C), 2(D), and 2(E), after the pulse test, multiple longitudinal wrinkles appear at the crimping point. Figure 2(E) shows fewer wrinkles, while Figure 2(D) shows the most wrinkles, which are stacked together. This indicates that the fatigue resistance of PTFE prepared using the process of this invention is significantly better than that of PTFE tubes prepared using ordinary processes. 3. Compression test:

[0131] The polytetrafluoroethylene tubes prepared in the above five examples (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4) were used to make samples of the same size. The samples were then placed on a pressure tester for pressure resistance testing. The test results are shown in Table 2 below.

[0132] Table 2

[0133]

[0134] As can be seen from Table 2, the polytetrafluoroethylene (PTFE) tube prepared in Example 1 of this invention is significantly superior to the PTFE tubes prepared in Comparative Examples 1-4. This is because this invention introduces pre-sintering and hot isostatic pressing (HIP) processes. Pre-sintering is carried out at a temperature of 200-300°C, which is lower than the melting point of the TFE / HFP copolymer (usually around 327°C) but much higher than its glass transition temperature Tg (approximately -80 to -100°C). This temperature range can promote the rearrangement of molecular chains in the material, promote the initial crystallization of the material, provide more crystal nuclei for subsequent high-temperature sintering, and promote more uniform crystallization. The uniform crystal structure can effectively disperse the applied pressure, avoid local stress concentration, and further improve the compressive strength of the material. At the same time, the HIP treatment is carried out under high pressure and high temperature, which can force the pores in the material to close, further improving the density of the material and significantly improving the mechanical properties of the material, especially the compressive strength. 4. Bending detection:

[0135] The polytetrafluoroethylene tubes prepared in the above five examples (Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4) were sampled with the same size and installed on a bending test device according to the bending radius required by the AS standard. The bending test was carried out. Table 3 shows the change of the inner diameter of each sample before and after bending. The change rate of the inner diameter = (inner diameter after bending - inner diameter before bending) / inner diameter before bending.

[0136] Table 3

[0137] As can be seen from Table 3, the change rate of the inner diameter after the bending test in Example 1 of the present invention is only 4%, while the change rate of the inner diameter before and after bending in Comparative Examples 1-4 all exceed 15%. In particular, although Comparative Example 3 has the same formula as Example 1 of the present invention, the preparation process is different, and its change rate of the inner diameter before and after bending even reaches 20%. Although Comparative Example 4 did not use the same copolymer-modified polytetrafluoroethylene as Example 1 of the present invention, it used the same preparation process, and its change rate of the inner diameter before and after bending was 17.92%. Although this change rate is greater than that of Example 1, it is less than that of the other comparative examples. This shows that the polytetrafluoroethylene pipe prepared by the present invention also has good bending strength. 5. Tensile porosity index:

[0138] The tensile porosity index mainly measures the change in specific gravity of a sample before and after stretching. Typically, the prepared polytetrafluoroethylene (PTFE) tube is stretched to 200% of its original length within 1–1.5 minutes, and then the specific gravity of the unstretched and stretched samples is measured. The higher the tensile porosity index, the more pores and permeability the material has, and the worse its resistance to stress cracking. (The volume can be calculated using the water displacement method). Three sample tubes were taken for each embodiment for testing, and the test results are shown in Table 4 below.

[0139] Table 4

[0140] As can be seen from Table 4, the tensile porosity index in Example 1 of the present invention is only between 0.12% and 0.17%, indicating that the material has fewer pores, better density and uniformity, and lower permeability; while Comparative Example 3 even reaches more than 1%, indicating that the tube material prepared by it has more internal pores, poor density, and higher permeability.

[0141] In summary, the above test results demonstrate that the PTFE tube prepared in Example 1 of this invention exhibits superior mechanical properties such as fatigue resistance, compressive strength, and flexural strength compared to the PTFE tubes prepared in Comparative Examples 1-4. Furthermore, Example 1 of this invention also shows a lower tensile porosity index, indicating fewer internal pores, better material uniformity and density, and superior impermeability. This demonstrates that the PTFE tube prepared using the formula and preparation process disclosed in this invention improves the material's impermeability while maintaining other mechanical properties, resulting in lower permeability.

[0142] The present invention has provided a detailed description of a low-permeability polytetrafluoroethylene (PTFE) tube and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these examples are merely for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A low-permeability polytetrafluoroethylene (PTFE) pipe, characterized in that, It is made from raw materials containing the following parts by weight: 90-95 parts of TFE / HFP copolymer, 2-5 parts of additives, 1-3 parts of nucleating agent, 0.5-1 part of antioxidant, and 0.1-1 part of antistatic agent.

2. The low-permeability polytetrafluoroethylene pipe according to claim 1, characterized in that, The composition includes 94 parts of TFE / HFP copolymer, 3 parts of additives, 2 parts of nucleating agent, 0.5 parts of antioxidant, and 0.5 parts of antistatic agent.

3. The low-permeability polytetrafluoroethylene pipe according to claim 1, characterized in that, The additive is one of paraffin oil, zinc stearate, and silicone oil; the nucleating agent is one of triphenyl phosphite, talc, silica, and calcium carbonate; the antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant; and the antistatic agent is one of bis(octadecyl)dimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

4. The low-permeability polytetrafluoroethylene pipe according to claim 1, characterized in that, The preparation method of the TFE / HFP copolymer is as follows: S1. Prepare raw materials: Weigh TFE, HFP and BPO according to the mass ratio; S2. Mixing raw materials: Add the TFE and HFP weighed in step S1 to a high-speed mixer and mix at 1000 rpm for 5 to 8 minutes. Then add BPO and continue stirring for 5 to 6 minutes to obtain a uniformly mixed material. S3. Polymerization reaction: Add the mixture from step S2 into a high-pressure reactor, place the high-pressure reactor in a heating furnace to heat and pressurize it, and react for 4 to 6 hours at a temperature of 80~100°C and a pressure of 20~40MPa. During the reaction, take a sample every hour and monitor the conversion rate by GPC or NMR. When the conversion rate reaches 85~95%, stop heating and pressurizing, allow it to cool naturally to room temperature, release the pressure in the high-pressure reactor, open the high-pressure reactor and take out the reaction product. S4. Cooling and drying: The reaction product in step S3 is naturally cooled to room temperature, and then the cooled product is placed in a vacuum drying oven and dried at 60~70℃ for 24h to obtain the dried copolymer; S5. Granulation: The dried copolymer from step S4 is added to a twin-screw granulator and granulated under the conditions of screw speed of 300 rpm, heating section temperature of 300°C and cooling section temperature of 200°C to obtain copolymer-modified polytetrafluoroethylene powder, namely: TFE / HFP copolymer.

5. The low-permeability polytetrafluoroethylene pipe according to claim 4, characterized in that, In step S1, the mass ratio of TFE to HFP is (90~95):(5~10); the BPO is 0.2%~0.8% of the total mass of TFE and HFP.

6. The low-permeability polytetrafluoroethylene pipe according to claim 5, characterized in that, In step S1, the mass ratio of TFE to HFP is 95:5, and the BPO is 0.5% of the total mass of TFE and HFP.

7. The low-permeability polytetrafluoroethylene pipe according to claim 4, characterized in that, In step S5, the particle size of the polytetrafluoroethylene powder is 0.3~0.4mm.

8. The method for preparing the low-permeability polytetrafluoroethylene tube according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Weigh out the TFE / HFP copolymer, additives and nucleating agent, antioxidant and antistatic agent according to the weight parts for later use; (2) After mixing the TFE / HFP copolymer, additives, nucleating agents, antioxidants and antistatic agents from step (1) in a high-speed mixer, store them at 10~15℃ for at least 24 hours. (3) Place the mixture stored for a period of time in step (2) into a preforming machine and press it into shape under a pressure of 5~8MPa and a compression rate of 40~50mm / min to obtain a blank; (4) Place the blank from step (3) on an extruder and extrude it at a material chamber temperature of 40~50℃, a die temperature of 50~60℃, and an extrusion rate of 80~100mm / min to obtain a green tube blank. (5) After drying and pre-sintering the green tube blank in step (4), the green tube blank is then subjected to hot isostatic pressing treatment to obtain a low-permeability polytetrafluoroethylene tube.

9. The method for preparing a low-permeability polytetrafluoroethylene pipe according to claim 8, characterized in that, In step (5), the drying temperature is 80~150℃ and the time is 20~24h; the pre-sintering temperature is 200~300℃ and the sintering time is 1.5~2.5h; the hot isostatic pressing treatment is 60~80MPa, the temperature is 350~400℃ and the time is 1~2h.

10. The method for preparing a low-permeability polytetrafluoroethylene pipe according to claim 9, characterized in that, In step (5), the drying temperature is 120℃ and the time is 22h; the pre-sintering temperature is 250℃ and the sintering time is 2h; the hot isostatic pressing treatment has a pressure of 70MPa, a temperature of 380℃ and a time of 1.5h.

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