PFA large-diameter heat-shrinkable tube and preparation method and application thereof

Abstract

The application discloses a PFA large-diameter heat-shrinkable tube and a preparation method and application thereof, and belongs to the technical field of high polymer materials. The preparation method of the PFA large-diameter heat-shrinkable tube comprises the following steps: PFA resin is plasticized by being heated and extruded through an extruder, a pipe blank is extruded through an extrusion die, the pipe blank is subjected to equi-proportion stretching, vacuum forming, cooling and setting to prepare a PFA base pipe; the PFA base pipe is heated, kept warm and cooled; and the PFA large-diameter heat-shrinkable tube is prepared through the following steps of inflation forming and cooling setting: the PFA base pipe is loaded into an inflation clamp, heated, inflated, kept pressure and cooled and set. The outer diameter of the heat-shrinkable tube base pipe prepared by the application is 80mm to 100mm, the wall thickness is 0.5 to 0.8mm, the thin-walled pipe is prepared, the inflation rate is 40%, the diameter is 112mm to 140mm, the length is 1m and 1.5m, the surface of the PFA large-diameter heat-shrinkable tube is smooth and smooth without folds, and the PFA large-diameter heat-shrinkable tube is suitable for various roller coating and joint protection.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a PFA large-diameter heat shrink tube, its preparation method, and its application. Background Technology

[0002] PFA is a copolymer of tetrafluoroethylene and perfluoroalkyl ethers. It has excellent corrosion resistance, excellent high and low temperature resistance, and good elongation, making it a rare functional polymer material. It is widely used in corrosion-resistant applications such as storage tank linings, chemical pipeline linings, linings of various valves, and heat exchangers for chemical reagents in the chemical industry.

[0003] PFA is selected to prepare large-diameter heat shrink tubing. Compared with PVC and polyethylene heat shrink tubing, it can improve the service temperature, mechanical strength and have the best non-stick properties. Compared with PTFE heat shrink tubing, it has better density and can prevent water vapor penetration and corrosive gas corrosion.

[0004] The preparation of large-diameter PFA heat shrink tubes is extremely difficult. It is affected by many factors, such as raw material selection, extruder technical parameters, extrusion die parameters, extrusion process parameters, base tube extrusion molding, base tube heat treatment, base tube, blow molding, cooling and shaping, which have delayed the development and research.

[0005] Existing technology discloses a blow-forming method for PFA heat shrink tubing, which uses an intermittent blow-forming process to prepare heat shrink tubing with an inner diameter of 5–14.5 mm. However, this process is only suitable for preparing heat shrink tubing with a smaller diameter, and is not applicable to the preparation of large-diameter PFA heat shrink tubing with an outer diameter of 80 mm–100 mm, a wall thickness of 0.5–0.8 mm, and a blow-forming rate of 40%. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the defects and shortcomings of existing blow-blowing processes that cannot produce heat shrinkable tube base tubes with an outer diameter of 80mm to 100mm, a wall thickness of 0.5mm to 0.8mm, and a blow-blowing rate of 40%. This invention provides a method for preparing large-diameter PFA heat shrinkable tubes, which produces thin-walled base tubes with an outer diameter of 80mm to 100mm, a wall thickness of 0.5mm to 0.8mm, and a blow-blowing rate of 40%. The tubes also have diameters of 112mm to 140mm and lengths of 1m and 1.5m. When heat-shrinked at 200℃, the surface is smooth and free of creases, making them suitable for various roller wrapping and joint protection.

[0007] Another object of the present invention is to provide a large-diameter PFA heat shrink tube.

[0008] Another objective of this invention is to provide an application of PFA large-diameter heat shrink tubing in protecting large-diameter cable joints, covering rollers of large printing and dyeing equipment, and sealing natural gas pipeline joints.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a large-diameter PFA heat shrink tubing includes the following steps:

[0011] S1. Preparation of PFA base pipe: PFA resin is heated and plasticized by extrusion through an extruder, and a pipe blank is extruded through an extrusion die. After proportional stretching, vacuum forming, and cooling and shaping, a PFA base pipe is obtained.

[0012] S2. Heat treatment: Heat, hold, and cool the PFA base tube in S1;

[0013] S3. Blow molding and cooling: The PFA base tube from S2 is placed into the blow molding fixture, heated, blown, pressure held, and cooled to obtain a large-diameter PFA heat shrink tube.

[0014] In S1, the melt index of PFA resin is 1.5 g / 10 min to 2.5 g / 10 min.

[0015] In S1 of this invention, the PFA resin has a melt index of 1.5 g / 10 min to 2.5 g / 10 min, exhibiting a high degree of polymerization, uniform and orderly distribution of macromolecular chains, good molecular ductility (elongation 290–300%, ASTM D238 / 23℃), and excellent mechanical properties (tensile strength 29–31 kN / cm). 2 (ASTM D238 / 23℃), which facilitates stretch forming and secondary processing, and is suitable for the preparation of large-diameter PFA heat shrink tubing.

[0016] One of the functions of heat treatment in S2 is to eliminate the tensile stress generated during the preparation of the base tube due to traction and the thermal stress generated during the cooling process, and to overcome stress cracking during secondary processing and blowing.

[0017] The second function of heat treatment in S2 is to prevent the base tube from shrinking during intermittent blow-blowing assembly, or shrinking during the heating process, or causing the tube to retract at the plug port of the blow-blowing fixture due to shrinkage.

[0018] The base tube of the PFA large-diameter heat shrink tube prepared by the method of the present invention has an outer diameter of 80mm to 100mm and a wall thickness of 0.5 to 0.8mm; and PFA large-diameter heat shrink tubes with an inflation rate of 40%, a diameter of 112mm to 140mm, and lengths of 1m and 1.5m are prepared, which can meet the following quality requirements: the surface of the heat shrink tube is smooth and flat with a uniform color, without ripple marks, and the wall thickness is uniform. The wall thickness tolerance is allowed to be controlled within ±0.05mm when measured with a micrometer caliper.

[0019] Preferably, during the extrusion process, the temperatures of each section of the extruder are as follows: feeding temperature is 180–200°C, conveying temperature is 220–280°C, plasticizing temperature is 320–340°C, and compression temperature is 330–380°C.

[0020] The mold body temperature is 330-380℃, the mandrel temperature is 330-380℃, and the die temperature is 330-380℃.

[0021] In the extrusion molding process of the base tube, selecting a lower plasticizing temperature and a lower screw speed can avoid molecular chain degradation during plasticizing and stretching during cooling and shaping, which can cause molecular orientation and thus prevent the base tube from breaking during secondary blow-up processing.

[0022] Preferably, in S1, during the extrusion process, the screw speed is 5-3 rpm and the traction speed is 11-12 cm / min.

[0023] During the extrusion process, the traction method of the base tube is based on the patent ZL2015205135553, which describes the traction method of the inner core support of large-diameter thin-walled tubes.

[0024] Preferably, in S1, the compression ratio of the extrusion die cavity is less than or equal to 2; the forming stretch ratio of the pipe is less than or equal to 2.

[0025] The compression ratio of the extrusion die of the present invention is less than or equal to 2, which can prevent the PFA resin melt from undergoing molecular degradation due to frictional heating in the extrusion die cavity, thereby preventing a decrease in elongation.

[0026] This invention controls the forming stretch ratio of the tube to be less than or equal to 2 during the extrusion process, which can prevent the base tube melt from being stretched too much and causing orientation, and improve the blow molding effect during secondary processing.

[0027] Preferably, in S1, the length-to-diameter ratio of the extruder screw is 25:1, the compression ratio of the screw is 2.5:1, the screw is a constant pitch gradually deformed screw, and the screw diameter is 25mm.

[0028] The screw structure of the extrusion molding equipment affects the plasticizing quality of the PFA resin plasticized melt. In order to obtain a uniformly plasticized melt, ensure that the molecular structure of the plasticized melt is not damaged, and prevent the melt molecular chains from becoming shorter or decomposing and discoloring, the screw structure parameters of the present invention are selected.

[0029] Preferably, in S1, the screw and barrel of the extruder are made of nickel-based alloy GH113.

[0030] Preferably, in S1, the die body, mandrel, and die of the extrusion die are made of nickel-based alloy GH113.

[0031] During the extrusion process, the plasticized melt of PFA is extremely corrosive. Generally, high-temperature screw and barrel steels such as 38G-M.Ar or 45# steel cannot withstand the corrosion of the plasticized melt and will rust. The screw and barrel of the extruder of this invention are made of nickel-based alloy GH113, which can prevent PFA from corroding the screw, barrel, and die.

[0032] The base tube prepared by the method of the present invention can meet the following quality requirements: pure texture, free of impurities and crystal points; uniform wall thickness, but the wall thickness tolerance is allowed to be controlled within ±0.02mm; no necking or bamboo-like phenomenon along the axial diameter of the base tube; smooth surface of the base tube, free of creases and scratches.

[0033] In S2, the base tube heating is carried out in a custom-designed hot water tank or steam tank that can be flushed with steam.

[0034] Preferably, in S2, the heating temperature is 95–100°C and the heating time is 30–35 min.

[0035] Preferably, in S3, the inflation temperature is 90-95℃, the inflation time is 2-5 min, the inflation pressure is 0.3-0.9 MPa, and the pressure holding time is 8-10 min.

[0036] In S3, the inflation rate of the heat shrink tube is (L1 - L2) × L2 × 100%, where L1 is the diameter of the heat shrink tube and L2 is the diameter of the base tube.

[0037] In S3, the present invention sets the blowing temperature to 90-95°C. Under this temperature condition, it has excellent forced high elastic deformation capability. Forced high elastic deformation is the movement of chain segments in the polymer macromolecular chain under the action of external force and dynamics such as stretching or blowing. However, once the kinetic energy is lost or the temperature is cooled, the chain segment movement is displaced and frozen. The frozen deformation is reversible. That is, after the external force is removed, when the ambient temperature rises to the kinetic energy required for the movement of molecular chain segments, it can be restored to the position and shape before the deformation, achieving the effect of thermal shrinkage.

[0038] In S3, the storage requirements for the PFA large-diameter heat shrink tubing prepared by this invention are as follows: packaged according to specifications, stored in a dry and cool place, away from heat sources, and protected from direct sunlight.

[0039] The present invention also protects the PFA large-diameter heat shrink tube prepared by the preparation method of any one of the above-described PFA large-diameter heat shrink tubes.

[0040] Preferably, the outer diameter of the PFA large-diameter heat shrinkable tube base tube of the present invention is 80mm to 100mm, the wall thickness is 0.5 to 0.8mm, the inflation rate is 40%, the diameter of the heat shrinkable tube is 112mm to 140mm, and the length is 1m and 1.5m.

[0041] This invention also protects the application of the aforementioned PFA large-diameter heat shrink tubing in protecting large-diameter cable joints, covering rollers of large printing and dyeing equipment, and sealing natural gas pipeline joints.

[0042] When in use, at a heat shrinking temperature of 200℃, the PFA large-diameter heat shrink tube prepared by this invention can be wrapped around the surface of the workpiece. Moreover, the surface of the heat shrink tube is smooth and flat without creases, making it suitable for wrapping various large-diameter thin-walled rollers and protecting joints.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] This invention discloses a method for preparing large-diameter PFA heat shrink tubing. Through specific process conditions, a thin-walled tube with an outer diameter of 80mm–100mm and a wall thickness of 0.5mm–0.8mm is prepared. This method produces large-diameter PFA heat shrink tubing with a blow-up rate of 40%, a diameter of 112mm–140mm, and lengths of 1m and 1.5m. When heat-shrinked at 200℃, the surface is smooth and free of creases. It is suitable for various roller wrapping and joint protection, and has excellent effects on wrapping large printing equipment rollers, sealing natural gas joints, and large-diameter cable joints. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the heat treatment chamber. In the diagram, 1-1: connector, 1-2: left and right shut-off valves, 1-3: bracket, 1-4: cover plate, 1-5: chamber body, 1-2: pressure gauge.

[0046] like Figure 1 As shown, the heat treatment chamber consists of connector 1-1, left and right shut-off valves 1-2, bracket 1-3, cover plate 1-4, chamber body 1-5, and pressure gauge 1-2.

[0047] The connecting pipe is made of 4" wall thickness stainless steel pipe, 100mm in length, with 1 / 2" external threads at both ends, and connects to stop valve 1-2, housing 1-5 and pressure gauge 1-2.

[0048] The shut-off valves 1-2 are 1 / 2" pneumatic valves used to control hot water discharge and steam pressure, ensuring control of heat treatment temperature and water volume.

[0049] Brackets 1-3 are made of stainless steel 15×15 square tubing and are used to place the PFA blow-up base tube and PFA large-diameter heat shrink tube blow-up clamp device.

[0050] Cover plates 1-4 are made of stainless steel.

[0051] The enclosures 1-5 are made of welded stainless steel plates.

[0052] Pressure gauges 1-2 are 1MPa pressure gauges, installed at the steam inlet of the heat treatment box, to monitor the steam pressure and control the water temperature inside the box.

[0053] Figure 2 This is a schematic diagram of an inflation clamp. In the diagram, 2-1: connecting pipe, 2-2: air shut-off valve, 2-3: pressure gauge, and 2-4: inclined conical plug.

[0054] like Figure 2 As shown, the clamping device consists of a connecting pipe 2-1, an air shut-off valve 2-2, a pressure gauge 2-3, an inclined conical plug 2-4, left and right horn-shaped connecting bodies, and an inflation cylinder.

[0055] Connector 2-1 is made of 4" wall thickness stainless steel pipe, 100mm in length (or customized as needed). Both ends are made with 1 / 2" external threads to connect to air shut-off valve 2-2, inclined cone plug 2-4 and pressure gauge 2-3.

[0056] Air shut-off valve 2-2 is a 1 / 2" pneumatic valve used to control the intake and exhaust of hot compressed air, and to control the amount of air during the blowing process, ensuring the air pressure of the device system and meeting the requirements of the blowing molding process.

[0057] Pressure gauge 2-3 is a 1MPa air pressure gauge, which is installed in the pipeline system of the device to observe the pressure changes during the blow molding process and control the molding pressure.

[0058] The left and right oblique conical plugs 2-4 are equipped with flanges that are consistent with the small end flange of the horn-shaped connector, which are suitable for bolt tightening. The root of the oblique conical surface has a 10mm straight surface with the same diameter as the inner diameter of the heat shrink tubing base pipe. The height of the oblique conical surface is 30mm and the oblique angle is 20°. A 20mm deep 1 / 2" screw hole is made in the center of the plug for pipe installation. A Φ10mm through hole is made in the center of the screw hole for conveying compressed air.

[0059] The left and right flared connectors are equipped with flanges at both ends. The small end flange matches the oblique conical end flange, while the large end flange mates with the inflatable cylinder flange. Both are secured with bolts. The small end diameter is equal to the outer diameter of the base pipe, and the large end inner diameter matches the inner diameter of the cylinder. The height of the left and right flared connectors is 1.5 times the diameter of the large-diameter thin-walled base pipe.

[0060] The inflator cylinder has flanges at both ends, which are respectively matched with the large end flange of the horn-shaped connector. Bolts are used for tightening during assembly.

[0061] The inner diameters of the inflation cylinders are 112mm, 122mm, and 140mm, and the lengths are 1m and 1.5m, respectively. The cylinders are arranged in an orderly manner at 90° with a spacing of 200mm. A Φ1mm through hole is made to remove air and water from the cylinder during inflation.

[0062] The left and right oblique conical plugs are assembled with the left and right horn-shaped connectors. The oblique part of the left and right oblique conical plugs is inserted into the inner hole of the base tube and matches the inner hole of the small end of the left and right horn-shaped connectors. When the bolts are tightened, they are in a sealed state and can ensure that there is no gas leakage during inflation, thus ensuring that the inflation of the base tube is completed smoothly. Detailed Implementation

[0063] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way.

[0064] Example 1

[0065] A method for preparing a large-diameter PFA heat shrink tubing includes the following steps:

[0066] S1. Preparation of PFA base pipe: PFA resin is heated and plasticized by extrusion through an extruder, and a pipe blank is extruded through an extrusion die. After proportional stretching, vacuum forming, and cooling and shaping, a PFA base pipe is obtained.

[0067] S2. Heat treatment: Heat the PFA base tube in S1, put the base tube into the heat treatment box and immerse it in water, turn on the steam, control the water temperature at 95℃, heat for 35 minutes, and take it out after naturally cooling to room temperature.

[0068] S3. Blow molding and cooling: The PFA base tube from S2 is placed into the blow molding fixture, heated, blown, pressure held, and cooled to obtain a large-diameter PFA heat shrink tube.

[0069] In S1, the melt index of PFA resin is 1.5 g / 10 min;

[0070] The compression ratio of the extrusion die cavity is equal to 2.

[0071] During the extrusion process, the forming stretch ratio of the tube is equal to 2.

[0072] During the extrusion process, the feeding temperature is 180℃, the conveying temperature is 220℃, the plasticizing temperature is 320℃, and the compression temperature is 330℃.

[0073] During the extrusion process, the die body temperature is 380℃, the mandrel temperature is 380℃, and the die temperature is 380℃.

[0074] The screw speed is 5 rpm, and the traction speed is 11 cm / min;

[0075] The outer diameter of the PFA base tube is 80mm, and the wall thickness is 0.2mm;

[0076] The extruder screw has a length-to-diameter ratio of 25:1, a compression ratio of 2.5:1, and is a constant pitch, gradually deformed screw. The screw diameter is 25 mm, and the screw and barrel of the extruder are made of nickel-based alloy GH113.

[0077] In S2, the heating temperature is 95℃ and the heating time is 35min;

[0078] In S3, the inflation temperature is 90℃, the inflation time is 3min, the inflation pressure is 0.3MPa, and the holding time is 8min.

[0079] The extrusion die has a die diameter of 120mm, a mandrel diameter of 158mm, a base tube size of Φ80mm×0.2mm, and a heat shrink tube size of Φ112mm×1m.

[0080] Example 2

[0081] A method for preparing a large-diameter PFA heat shrink tubing includes the following steps:

[0082] S1. Preparation of PFA base pipe: PFA resin is heated and plasticized by extrusion through an extruder, and a pipe blank is extruded through an extrusion die. After proportional stretching, vacuum forming, and cooling and shaping, a PFA base pipe is obtained.

[0083] S2. Heat treatment: Heat the PFA base tube in S1, put the base tube into the heat treatment box and immerse it in water, turn on the steam, control the water temperature at 100℃, heat for 30 minutes, and take it out after naturally cooling to room temperature.

[0084] S3. Blow molding and cooling: The PFA base tube from S2 is placed into the blow molding fixture, heated, blown, pressure held, and cooled to obtain a large-diameter PFA heat shrink tube.

[0085] In S1, the melt index of PFA resin is 1.8 g / 10 min;

[0086] The compression ratio of the extrusion die cavity is equal to 2.

[0087] During the extrusion process, the forming stretch ratio of the tube is equal to 2.

[0088] During the extrusion process, the feeding temperature is 200℃, the conveying temperature is 235℃, the plasticizing temperature is 325℃, and the compression temperature is 335℃.

[0089] During the extrusion process, the die body temperature is 380℃, the mandrel temperature is 380℃, and the die temperature is 380℃.

[0090] The screw speed is 2 rpm, and the traction speed is 12 cm / min;

[0091] The outer diameter of the PFA base tube is 90mm, and the wall thickness is 0.2mm;

[0092] The extruder screw has a length-to-diameter ratio of 25:1, a compression ratio of 2.5:1, and is a constant pitch, gradually deformed screw. The screw diameter is 25 mm, and the screw and barrel of the extruder are made of nickel-based alloy GH113.

[0093] In S2, the heating temperature is 100℃ and the heating time is 30min;

[0094] In S3, the inflation temperature is 95℃, the inflation time is 5min, the inflation pressure is 0.9MPa, and the holding time is 10min.

[0095] The extrusion die has a die diameter of 180mm, a mandrel diameter of 133.2mm, a base tube size of Φ90mm×0.2mm, and a heat shrink tube size of Φ122mm×1.5m.

[0096] Example 3

[0097] A method for preparing a large-diameter PFA heat shrink tubing includes the following steps:

[0098] S1. Preparation of PFA base pipe: PFA resin is heated and plasticized by extrusion through an extruder, and a pipe blank is extruded through an extrusion die. After proportional stretching, vacuum forming, and cooling and shaping, a PFA base pipe is obtained.

[0099] S2. Heat treatment: Heat the PFA base tube in S1, put the base tube into the heat treatment box and immerse it in water, turn on the steam, control the water temperature at 95℃, heat for 30 minutes, and take it out after naturally cooling to room temperature.

[0100] S3. Blow molding and cooling: The PFA base tube from S2 is placed into the blow molding fixture, heated, blown, pressure held, and cooled to obtain a large-diameter PFA heat shrink tube.

[0101] In S1, the melt index of PFA resin is 2.5 g / 10 min;

[0102] The compression ratio of the extrusion die cavity is equal to 2.

[0103] During the extrusion process, the forming stretch ratio of the tube is equal to 2.

[0104] During the extrusion process, the feeding temperature is 200℃, the conveying temperature is 220℃, the plasticizing temperature is 320℃, and the compression temperature is 330℃.

[0105] During the extrusion process, the die body temperature is 380℃, the mandrel temperature is 380℃, and the die temperature is 380℃.

[0106] The screw speed is 5 rpm, and the traction speed is 11 cm / min;

[0107] The outer diameter of the PFA base tube is 100mm, and the wall thickness is 0.8mm;

[0108] The extruder screw has a length-to-diameter ratio of 25:1, a compression ratio of 2.5:1, and is a constant pitch, gradually deformed screw. The screw diameter is 25 mm, and the screw and barrel of the extruder are made of nickel-based alloy GH113.

[0109] In S2, the heating temperature is 95℃ and the heating time is 30 minutes;

[0110] In S3, the inflation temperature is 90℃, the inflation time is 4min, the inflation pressure is 0.8MPa, and the holding time is 9min.

[0111] The extrusion die has a die diameter of 200mm, a mandrel diameter of 192.8mm, a base tube size of Φ100mm×0.8mm, and a heat shrink tube size of Φ140mm×1.5m.

[0112] Result detection

[0113] The quality of the base tube prepared by step S1 of the method of the present invention is as follows: the base tube is pure in texture, free of impurities and crystal points; the wall thickness of the base tube is uniform, but the wall thickness tolerance is allowed to be controlled within ±0.02mm; the base tube has no neck or bamboo joint phenomenon along the axial diameter direction; the surface of the base tube is smooth, without creases or scratches.

[0114] The quality of the PFA large-diameter heat shrink tube prepared by this invention is as follows: the surface of the heat shrink tube is smooth and flat with consistent color, no ripple marks, uniform wall thickness, and the wall thickness tolerance can be controlled within ±0.05mm when dry molecular weight measurement is used.

[0115] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a large-diameter PFA heat shrink tube, characterized in that, Includes the following steps: S1. Preparation of PFA base pipe: PFA resin is heated and plasticized by extrusion through an extruder, and a pipe blank is extruded through an extrusion die. After proportional stretching, vacuum forming, and cooling and shaping, PFA base pipe is obtained. S2. Heat treatment: Heat, hold, and cool the PFA base tube from S1; S3. Blow-in molding and cooling: The PFA base tube from S2 is placed into the blow-in fixture, heated, blow-in, pressure held, and cooled to obtain a large-diameter PFA heat shrink tube. In S1, the melt index of PFA resin is 1.5 ~ 2.5 g / 10 min; the compression ratio of the extrusion die cavity is less than or equal to 2, the forming elongation ratio of the pipe is less than or equal to 2; and the outer diameter of the PFA base pipe is 80 mm ~ 100 mm. In S2, the heating temperature is 95~100℃ and the heating time is 30~35min; In S3, the inflation temperature is 90~95℃ and the inflation pressure is 0.7~0.9MPa; the diameter of the PFA large-diameter heat shrink tube is 112mm~140mm.

2. The method for preparing PFA large-diameter heat shrink tubing as described in claim 1, characterized in that, In S1, during the extrusion process, the temperatures of each section of the extruder are as follows: feeding temperature 180~200℃, conveying temperature 260~280℃, plasticizing temperature 320~340℃, and compression temperature 370~380℃; die temperatures are as follows: die body temperature 370~380℃, mandrel temperature 370~380℃, and die nozzle temperature 370~380℃.

3. The method for preparing PFA large-diameter heat shrink tubing as described in claim 1, characterized in that, In S1, the screw speed is 5~7 rpm and the traction speed is 11~12 cm / min.

4. The method for preparing PFA large-diameter heat shrink tubing as described in claim 1, characterized in that, In S1, the length-to-diameter ratio of the extruder screw is 25:1, the compression ratio of the screw is 2.5:1, and the screw is a constant pitch gradually deformed screw; the screw diameter is 65mm, and the screw and barrel of the extruder are made of nickel-based alloy GH113.

5. The method for preparing PFA large-diameter heat shrink tubing as described in claim 1, characterized in that, In S3, the inflation time is 2-5 minutes and the pressure holding time is 8-10 minutes.

6. The PFA large-diameter heat shrinkable tube prepared by the preparation method of any one of claims 1 to 5.

7. The PFA large-diameter heat shrink tubing as described in claim 6, characterized in that, The PFA base tube has a wall thickness of 0.5 mm to 0.8 mm and an inflation rate of 40%. The length of the PFA large-diameter heat shrink tube is 1 m or 1.5 m.

8. The application of the PFA large-diameter heat shrink tubing as described in claim 7 in protecting large-diameter cable joints, covering rollers of large printing and dyeing equipment, and sealing natural gas pipeline joints.

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