Special rheological test instrument and test method for polytetrafluoroethylene paste extrusion

Abstract

The invention relates to the technical field of rheology testing, and particularly discloses a special rheology testing instrument and a testing method for polytetrafluoroethylene paste extrusion, which comprises a charging barrel, a casting blank cavity arranged at one end of the charging barrel, an extrusion cavity arranged at the other end of the charging barrel, a valve arranged between the casting blank cavity and the extrusion cavity, and a piston arranged in the casting blank cavity in a sliding manner, the driving device is connected with the piston; the runner module is detachably connected with the end part of one end, far away from the casting blank cavity, of the extrusion cavity; and a convergent runner connected with the extrusion cavity and a capillary runner connected with the convergent runner are formed in the runner module. According to the special rheological test instrument and test method for polytetrafluoroethylene paste extrusion, the real rheological behavior of polytetrafluoroethylene can be effectively tested, and guidance is provided for forming and manufacturing of polytetrafluoroethylene products.

Description

Technical Field

[0001] This invention relates to the technical field of rheological testing, and more specifically, to a rheological testing instrument and method specifically for polytetrafluoroethylene paste extrusion. Background Technology

[0002] The molding and processing of polytetrafluoroethylene (PTFE) typically involves first mixing the resin with lubricating oil to form a slurry, then casting a dense rod under constant pressure, and finally extruding the slurry through a converging flow channel in the die head. The extrusion rheological behavior of the slurry directly determines the quality of the preform and the performance of the extruded product.

[0003] Currently, the evaluation of the processing rheological properties of polymer materials mainly uses general-purpose high-pressure capillary rheometers. However, for the polytetrafluoroethylene (PTFE) paste extrusion process, this type of general-purpose equipment has the following drawbacks:

[0004] (1) Lack of billet casting function, sample state is out of sync with industrial production: General instruments usually directly fill the slurry for testing, while the PTFE process requires "constant pressure casting of billets" first. If the billet is prepared externally and then moved into the instrument, it is difficult to fill due to the matching of the billet length and size, and structural defects are easily generated during the transfer process. (2) Mismatch of extrusion channels: The channels of general instruments are usually single straight capillary tubes, which cannot simulate the process of controlling the deformation of the billet by the convergence degree of the die head in industrial production. (3) Insufficient wall slip correction: PTFE slurry is very prone to wall slip, and the correction algorithm and hardware structure of general instruments are often unable to accurately eliminate this error, resulting in distortion of rheological parameters. Summary of the Invention

[0005] The purpose of this invention is to provide a rheological testing instrument and method specifically for polytetrafluoroethylene (PTFE) paste extrusion, which can effectively test the true rheological behavior of PTFE.

[0006] This invention is achieved through the following technical solution: The rheological testing instrument and method for polytetrafluoroethylene paste extrusion of this invention includes a barrel, a casting cavity at one end of the barrel, an extrusion cavity at the other end of the barrel, a valve between the casting cavity and the extrusion cavity, a piston slidably disposed in the casting cavity, a driving device connected to the piston, and a flow channel module detachably connected to the end of the extrusion cavity away from the casting cavity; the flow channel module has a converging flow channel connected to the extrusion cavity and a capillary flow channel connected to the converging flow channel.

[0007] Furthermore, the valve is a gate valve; the gate valve includes a valve body disposed on the outer wall of the material cylinder, a slide plate slidably disposed in the valve body and the material cylinder, and a drive rod connected to the slide plate; the axial direction of the material cylinder is perpendicular to the plane where the slide plate is located.

[0008] Furthermore, the driving device includes a hydraulic press connected to the piston; the hydraulic press is used to drive the piston to move axially along the barrel.

[0009] Furthermore, the inner diameter of the converging flow channel near the extrusion chamber is the same as the inner diameter of the extrusion chamber, and the inner diameter of the converging flow channel near the capillary flow channel is the same as the inner diameter of the capillary flow channel. Preferably, the inner diameter of the barrel is 30 mm, the total length is 450 mm, the casting cavity length is 200 mm, and the wall thickness is 30 mm.

[0010] Furthermore, the convergence angle of the converging channel is 20-90 degrees; the diameter of the capillary channel is 2-6 mm; and the length-to-diameter ratio of the capillary channel is 10-40:1.

[0011] Furthermore, it also includes a pressure detection system for detecting the pressure of the barrel and the flow channel module.

[0012] Furthermore, the pressure detection system includes a first pressure sensor disposed on the inner wall of the casting cavity, a second pressure sensor disposed at the inlet of the convergent flow channel, and a third pressure sensor disposed at the inlet of the capillary flow channel.

[0013] The present invention also provides a testing method based on the above-mentioned rheological testing instrument for polytetrafluoroethylene paste extrusion, comprising the following steps: (1) Close the valve and feed the slurry of polytetrafluoroethylene resin and lubricating oil into the casting cavity; (2) Using a drive device to push the piston with a constant pressure P, the slurry is squeezed and then held under pressure to form a bar blank; (3) Open the valve and use the drive device to drive the piston to push the billet into the extrusion chamber, and then continue to push it into the flow channel module; (4) Detect the pressure of the second pressure sensor through the pressure detection system. P 0 and the pressure of the third pressure sensor P 1; (5) Under the same barrel temperature and piston movement speed, replace the flow channel modules with different length-to-diameter ratios and repeat steps (3)-(4) to obtain multiple sets. P 0, P 1. Data; (6) Eliminate the inlet effect based on the collected data and use the Mooney method for wall slip correction to calculate the real rheological parameters.

[0014] Furthermore, the method for eliminating the entry effect in step (6) is as follows: Calculate the inlet pressure drop ΔP entry =P 0 P 1; Calculate the pressure drop in a pure capillary tube ΔP cap =P 1; Among them, the inlet pressure dropped ΔP entry Eliminated, using only pure capillary pressure drop ΔP cap Subsequent shear rheological calculations were then performed.

[0015] Furthermore, step (6) of Mooney's method for wall slip correction specifically includes: according to the formula

[0016] Calculate the apparent shear rate; According to the formula

[0017] Calculate the apparent wall shear stress, where R is the capillary radius, L is the capillary length, and Q is the slurry volume flow rate; The apparent wall shear stress τ w,a Plotting a graph with 1 / R as the x-axis and performing a linear fit yields the fitted equation.

[0018] Extrapolate to 1 / (L / R At point )=0, the true wall shear stress under no-slip condition is obtained.

[0019] Combining volumetric flow rate, according to the formula

[0020] The wall sliding velocity was calculated; In the formula, Q / (πR) 2 ) represents the average apparent velocity of the fluid within the capillary. true ×R / 3 is the average velocity caused by internal shearing of the fluid. The difference between the two is the relative slip velocity between the wall and the fluid. The larger the difference, the more significant the slip. Further according to the formula

[0021] The actual shear rate is calculated; Finally, according to the formula

[0022] To obtain the true viscosity.

[0023] The technical solution of this invention has at least the following advantages and beneficial effects: The rheological testing instrument and method for polytetrafluoroethylene (PTFE) paste extrusion of this invention involves adding PTFE slurry into the casting cavity (the piston needs to be fully withdrawn first), using a driving device to push the piston to extrude the PTFE slurry into a rod, and then using the piston to push the rod into the extrusion cavity and flow channel module. The rod is pressurized into the converging flow channel and capillary flow channel. The slurry is added once, and the densification of the casting is automatically completed without sample transfer. This solves the problems of difficulty in loading rods with general-purpose instruments, difficulty in matching rod size with barrel size, and defects that may occur during the transfer process due to the loose structure of the rod. By measuring the dimensional parameters of the barrel and flow channel module, as well as the pressure data therein, the true viscosity of the PTFE material can be effectively obtained. By changing the flow channel module with different parameters, the extrusion rheological behavior of PTFE slurry with different formulations can be accurately reflected, enabling experimental testing to guide industrial production. In addition, the strip extruded by the instrument can be pressed into PTFE sheets by a calender, and further uniaxial or biaxial hot stretching can produce PTFE microporous membrane materials, thereby verifying the influence of the extrusion rheological behavior of the slurry on subsequent molding and the structural properties of sheets and membranes. Attached Figure Description

[0024] Figure 1 A schematic diagram of the structure of a rheological testing instrument for polytetrafluoroethylene paste extrusion provided in Embodiment 1 of the present invention.

[0025] Icons: 10-Barrel, 11-Casting cavity, 12-Extrusion cavity, 13-Valve, 15-Piston, 16-Drive device, 20-Flow channel module, 21-Converging flow channel, 22-Capillary flow channel, 31-First pressure sensor, 32-Second pressure sensor, 33-Third pressure sensor. Detailed Implementation

[0026] Example 1 The following description, in conjunction with specific embodiments, further illustrates the point, as shown in the appendix. Figure 1As shown, the rheological testing instrument and method for polytetrafluoroethylene paste extrusion in this embodiment includes a barrel 10, a casting cavity 11 at one end of the barrel 10, an extrusion cavity 12 at the other end of the barrel 10, a valve 13 between the casting cavity 11 and the extrusion cavity 12, a piston 15 slidably disposed in the casting cavity 11, a drive device 16 connected to the piston 15, and a flow channel module 20 detachably connected to the end of the extrusion cavity 12 away from the casting cavity 11; the flow channel module 20 has a converging flow channel 21 section connected to the extrusion cavity 12 and a capillary flow channel 22 section connected to the converging flow channel 21 section. Specifically, the dedicated rheological testing instrument and method for polytetrafluoroethylene (PTFE) paste extrusion involves feeding PTFE slurry into the casting cavity 11, using a drive device 16 to push a piston 15 to extrude the PTFE slurry into a rod. The piston 15 then pushes the rod into the extrusion cavity 12 and the flow channel module 20. The rod, under pressure, enters the converging flow channel 21 and the capillary flow channel 22. The slurry is added once, automatically completing the densification of the casting, eliminating sample transfer. This solves the problems of difficulty in loading rods with general-purpose instruments, difficulty in matching rod dimensions to the barrel 10 size, and potential defects caused by the loose structure of the rod during the transfer process. By measuring the dimensional parameters of the barrel 10 and the flow channel module 20, as well as the pressure data within them, the true viscosity of the PTFE material can be effectively obtained. By changing the flow channel module 20 with different parameters, the extrusion rheological behavior of PTFE slurry with different formulations can be accurately reflected, enabling experimental testing to guide industrial production.

[0027] In this embodiment, valve 13 is a gate valve; the gate valve includes a valve body disposed on the outer wall of the barrel 10, a slide plate slidably disposed in the valve body and the barrel 10, and a drive rod connected to the slide plate; the axial direction of the barrel 10 is perpendicular to the plane where the slide plate is located. Specifically, the slide plate in the gate valve can be completely perpendicular to the axial direction of the barrel 10, and the slide plate is a completely flat plane, which is more conducive to billet forming.

[0028] The drive device 16 in this embodiment includes a hydraulic press connected to the piston 15; the hydraulic press is used to drive the piston 15 to move axially along the barrel 10.

[0029] In this embodiment, the inner diameter of the converging flow channel 21 near the extrusion chamber 12 is the same as the inner diameter of the extrusion chamber 12, and the inner diameter of the converging flow channel 21 near the capillary flow channel 22 is the same as the inner diameter of the capillary flow channel 22. Specifically, this effectively prevents the sidewall of the billet from being scratched, and the barrel 10 is a one-piece structure. The flow channel module 20 can be connected to the barrel 10 by threads, and a sealing structure needs to be provided at the contact surface.

[0030] In this embodiment, the convergence angle of the converging channel 21 is 20-90 degrees; the diameter of the capillary channel 22 is 2-6 mm, and the length-to-diameter ratio of the capillary channel 22 is 10-40:1. The length-to-diameter ratio is mainly in various combinations such as 10:1 / 20:1 / 30:1 / 40:1.

[0031] This embodiment also includes a pressure detection system for detecting the pressure of the barrel 10 and the flow channel module 20. The pressure detection system includes a first pressure sensor 31 located on the inner wall of the casting cavity 11, a second pressure sensor 32 located at the inlet of the converging flow channel 21, and a third pressure sensor 33 located at the inlet of the capillary flow channel 22. The pressure sensor accuracy is 0.1%FS. Heating jackets need to be installed on the outer walls of the barrel 10 and the flow channel module 20 to heat them; therefore, multiple temperature sensors also need to be installed in the barrel 10 and the flow channel module 20 to monitor the temperature.

[0032] Example 2 This embodiment provides a testing method for a dedicated rheological testing instrument for polytetrafluoroethylene paste extrusion based on Embodiment 1, including the following steps: (1) Close the valve and feed the slurry of polytetrafluoroethylene resin and lubricating oil into the casting cavity; (2) Using a drive device to push the piston with a constant pressure P, the slurry is squeezed and then held under pressure to form a bar blank; (3) Open the valve and use the drive device to drive the piston to push the billet into the extrusion chamber, and then continue to push it into the flow channel module; (4) Detect the pressure of the second pressure sensor through the pressure detection system. P 0 and the pressure of the third pressure sensor P 1; (5) Under the same barrel temperature and piston movement speed, replace the flow channel modules with different length-to-diameter ratios and repeat steps (3)-(4) to obtain multiple sets. P 0, P 1. Data; (6) Eliminate the inlet effect based on the collected data and use the Mooney method for wall slip correction to calculate the real rheological parameters.

[0033] Furthermore, the method for eliminating the entry effect in step (6) is as follows: Calculate the inlet pressure drop ΔP entry =P 0 P 1; Calculate the pressure drop in a pure capillary tube ΔP cap =P 1; Among them, the inlet pressure dropped ΔP entry Eliminated, using only pure capillary pressure drop ΔP cap Subsequent shear rheological calculations were then performed.

[0034] Furthermore, step (6) of Mooney's method for wall slip correction specifically includes: according to the formula

[0035] Calculate the apparent shear rate; According to the formula

[0036] Calculate the apparent wall shear stress, where R is the capillary radius, L is the capillary length, and Q is the slurry volume flow rate; The apparent wall shear stress τ w,a Plotting a graph with 1 / R as the x-axis and performing a linear fit yields the fitted equation.

[0037] Extrapolate to 1 / (L / R At point )=0, the true wall shear stress under no-slip condition is obtained.

[0038] Combining volumetric flow rate, according to the formula

[0039] The wall sliding velocity was calculated; In the formula, Q / (πR) 2 ) represents the average apparent velocity of the fluid within the capillary. true ×R / 3 is the average velocity caused by internal shearing of the fluid. The difference between the two is the relative slip velocity between the wall and the fluid. The larger the difference, the more significant the slip. Further according to the formula

[0040] The actual shear rate is calculated; Finally, according to the formula

[0041] To obtain the true viscosity.

[0042] Experimental Example 1 The flowability of polytetrafluoroethylene was tested using the testing instruments in Example 1 and the testing methods in Example 2. The initial slurry was prepared by mixing polytetrafluoroethylene resin and paraffin oil at a mass ratio of 8:2.

[0043] (1) Instrument parameters: the inner diameter of the barrel is D=30mm, the pressure of the billet is set to 10MPa, and the holding time is 5min; select a composite module with a convergence angle of 45° and a capillary channel inner diameter of d=4mm, and equip it with three capillary tubes with length-to-diameter ratios of L / d=10:1, 20:1, and 30:1. (2) Test temperature and piston speed: The test temperature was set to 50℃, and the piston constant speed was set to 2mm / min, 10mm / min, 20mm / min and 30mm / min. The rheological parameters at different speeds were tested respectively. (3) Casting and extrusion test: The uniformly mixed polytetrafluoroethylene slurry was added to the casting cavity of the barrel at one time. The instrument was started and the temperature control system stabilized the slurry temperature to 50℃. The hydraulic press drove the piston to extrude the slurry at a constant pressure of 10MPa and held the pressure for 5min to complete the formation of a dense cylindrical billet. The piston was driven in sequence to push the billet to be extruded at speeds of 2mm / min, 10mm / min, 20mm / min and 30mm / min. At each speed, a capillary tube with L / d=10:1, 20:1 and 30:1 was used to complete the test and collect the inlet pressure of the convergent flow channel. P 0. Capillary inlet pressure P 1; (4) Error correction and parameter calculation: The measurement and control system automatically eliminates the inlet effect and obtains the pure capillary pressure drop; the true wall shear stress and true shear rate are obtained by linear fitting using the Mooney method, and the true viscosity is calculated. (5) Test results: The true viscosity of the slurry decreased significantly with increasing shear rate. At a shear rate of 10 s, the viscosity decreased significantly. 1 At that time, the measured apparent viscosity was 2.12 × 10⁻⁶. 5 The actual viscosity, calculated after correction, is 1.96 × 10 Pa·s. 4 Pa·s, proving that the correction method of the present invention can effectively eliminate the error caused by wall slippage.

[0044] Experiment Example 2 Using the test process in Experiment 1, the rheological properties of PTFE slurries with different lubricant ratios (mass ratios of 6:4, 7:3, 8:2, and 9:1) were tested to simulate the convergence angle of the 60° flow channel in the industrial production of PTFE.

[0045] Test results show that when the lubricating oil ratio is 8:2, the shear thinning effect of the slurry is moderate, the extrusion pressure is 2MPa, and the green body is densely formed without defects such as cracking or peeling. When the lubricating oil ratio is too high (6:4), the slurry viscosity is too low, the wall slippage is serious, and the extruded green body is unstable. When the lubricating oil ratio is too low (9:1), the slurry viscosity is too high, the extrusion pressure reaches 4MPa, and it is easy to cause internal cracking of the green body. The strip extruded by the instrument is used to prepare polytetrafluoroethylene microporous membrane material through calendering and hot stretching. When the lubricating oil ratio is 8:2, the membrane material has the best pore structure uniformity, mechanical strength and elongation at break.

[0046] Based on the test results, the optimal lubricant ratio was determined to be 8:2, and the extrusion speed was set to 20 mm / min. Using the same raw material type, lubricant ratio, extrusion speed, and extruder head convergence angle, verification on an industrial production device showed that the produced polytetrafluoroethylene microporous membrane exhibited optimal pore structure uniformity, mechanical strength, and elongation at break. These results were consistent with those obtained using the testing instrument in Example 1 and the testing method in Example 2, proving that the instrument test results of this invention can directly guide industrial production.

[0047] Comparative Example 1 (using a conventional high-pressure capillary rheometer to directly test the slurry before casting). The flowability of polytetrafluoroethylene (PTFE) was tested using a conventional high-pressure capillary rheometer. The initial slurry was prepared by mixing PTFE resin and paraffin oil at a mass ratio of 8:2.

[0048] (1) Instrument parameters: The high-pressure capillary rheometer has no billet cavity; the inner diameter of the barrel is D=30mm; a composite module with a convergence angle of 45° and a capillary channel inner diameter of d=4mm is selected, and three capillaries with length-to-diameter ratios L / d=10:1, 20:1 and 30:1 are equipped. (2) Test temperature and piston speed: The test temperature was set to 50℃, and the piston constant speed was set to 2mm / min, 10mm / min, 20mm / min and 30mm / min. The rheological parameters at different speeds were tested respectively. (3) Extrusion test: The uniformly mixed polytetrafluoroethylene slurry was added to the barrel at one time, the instrument was started, and the temperature control system stabilized the slurry temperature to 50℃; the piston was driven in sequence to push the slurry to extrude at a speed of 2mm / min, 10mm / min, 20mm / min, and 30mm / min. At each speed, a capillary tube with L / d=10:1, 20:1, and 30:1 was used to complete the test, and the inlet pressure of the convergent flow channel was collected. P 0. Capillary inlet pressure P 1; (4) Error correction and parameter calculation: The measurement and control system automatically eliminates the inlet effect and obtains the pure capillary pressure drop; the true wall shear stress and true shear rate are obtained by linear fitting using the Mooney method, and the true viscosity is calculated. (5) Test results: The true viscosity of the slurry decreased significantly with increasing shear rate. At a shear rate of 10 s, the viscosity decreased significantly. 1 At that time, the measured apparent viscosity was 1.43 × 10⁻⁶. 4 The actual viscosity, calculated after correction, is 1.27 × 10 Pa·s. 4 The measured apparent viscosity and true viscosity were both lower than those obtained using the testing instrument in Example 1. Analysis suggests that the slurry, not being cast into a preform, lacked intermolecular entanglement, making it more fluid.

[0049] Comparative Example 2 (using a conventional high-pressure capillary rheometer to directly test the slurry without a cast billet) Using the test process in Comparative Example 1, the rheological properties of PTFE slurries with different lubricant ratios (mass ratios of 6:4, 7:3, 8:2, and 9:1) were tested to simulate the convergence angle of the PTFE head flow channel in industrial production.

[0050] Test results show that the apparent viscosity and true viscosity of all slurries with different lubricating oil ratios, as measured by a conventional high-pressure capillary rheometer, are lower than those measured by the instrument used in Example 1. Furthermore, due to the lack of in-molecular contact caused by the absence of a cast billet, all of them exhibited problems with extrusion instability.

[0051] The strip extruded by the instrument, through calendering and hot stretching, produced polytetrafluoroethylene microporous membrane materials. All of them had the problem of poor pore structure uniformity. The mechanical strength and elongation at break were more than 20% lower than those of Experimental Example 2, proving that the data measured by the conventional high-pressure capillary rheometer cannot directly guide industrial production.

[0052] Comparative Example 3 (The slurry was precast into a billet and then tested using a conventional high-pressure capillary rheometer) The flowability of polytetrafluoroethylene (PTFE) was tested using a conventional high-pressure capillary rheometer. The initial slurry was prepared by mixing PTFE resin and paraffin oil at a mass ratio of 8:2. The slurry was then cast into rod-shaped billets with a diameter of 30 mm using specialized casting equipment. The casting pressure was set at 10 MPa, and the holding time was 5 minutes.

[0053] (1) Instrument parameters: The high-pressure capillary rheometer has no billet cavity; the inner diameter of the barrel is D=30mm; a composite module with a convergence angle of 45° and a capillary channel inner diameter of d=4mm is selected, and three capillaries with length-to-diameter ratios L / d=10:1, 20:1 and 30:1 are equipped. (2) Test temperature and piston speed: The test temperature was set to 50℃, and the piston constant speed was set to 2mm / min, 10mm / min, 20mm / min and 30mm / min. The rheological parameters at different speeds were tested respectively. (3) Extrusion test: The pre-cast billet is placed into the barrel, the instrument is started, and the temperature control system stabilizes the slurry temperature to 50℃; the piston is driven sequentially to push the slurry to be extruded at speeds of 2mm / min, 10mm / min, 20mm / min, and 30mm / min. At each speed, a capillary tube with L / d=10:1, 20:1, and 30:1 is used to complete the test, and the inlet pressure of the convergent flow channel is collected. P 0. Capillary inlet pressure P 1; (4) Error correction and parameter calculation: The measurement and control system automatically eliminates the inlet effect and obtains the pure capillary pressure drop; the true wall shear stress and true shear rate are obtained by linear fitting using the Mooney method, and the true viscosity is calculated. (5) Test results: The true viscosity of the slurry decreased significantly with increasing shear rate. At a shear rate of 10 s, the viscosity decreased significantly. 1 At that time, the measured apparent viscosity was 1.72 × 10⁻⁶. 4 The actual viscosity, calculated after correction, is 1.57 × 10 Pa·s. 4 The measured apparent viscosity and true viscosity were both lower than those obtained using the testing instrument in Example 1, but higher than those in Comparative Example 1. Analysis suggests that pre-casting the slurry into a billet before transferring it into the high-pressure capillary rheometer may have caused defects in the billet transfer process due to limitations in the overall design of conventional instruments, or the difference between the billet size and the inner diameter of the conventional instrument's barrel, resulting in lower measured viscosity data.

[0054] Comparative Example 4 (The slurry was precast into a billet and then tested using a conventional high-pressure capillary rheometer) Using the test process in Comparative Example 3, the rheological properties of PTFE slurries with different lubricant ratios (mass ratios of 6:4, 7:3, 8:2, and 9:1) were tested to simulate the convergence angle of the PTFE machine head flow channel in industrial production.

[0055] Test results show that the apparent viscosity and true viscosity of slurries with all lubricating oil proportions, after pre-casting, are lower than those measured by the testing instrument in Example 3.

[0056] When the lubricating oil ratio is 8:2, the shear thinning effect of the slurry is moderate, the extrusion pressure is 2MPa, and the billet is densely formed. However, due to the overall design limitations of the conventional high-pressure capillary rheometer, defects occur during the billet transfer process, or due to the difference between the size of the pre-cast billet and the inner diameter of the rheometer barrel, local flow instability occurs in the extrudate. When the lubricating oil ratio is too high (6:4), the slurry viscosity is too low, the wall slippage is severe, and the extruded billet is unstable. When the lubricating oil ratio is too low (9:1), the slurry viscosity is too high, the extrusion pressure reaches 4MPa, and it is easy to cause internal cracking of the billet.

[0057] The strip extruded by the instrument was used to prepare polytetrafluoroethylene microporous membrane materials through calendering and hot stretching. All of them had the problem of poor pore structure uniformity. The mechanical strength and elongation at break were more than 5% lower than those of Experiment 2, which proves that the data measured by the conventional high-pressure capillary rheometer cannot directly guide industrial production.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rheological testing instrument specifically for polytetrafluoroethylene paste extrusion, characterized in that: The device includes a barrel, a casting cavity at one end of the barrel, an extrusion cavity at the other end of the barrel, a valve between the casting cavity and the extrusion cavity, a piston slidably disposed in the casting cavity, a drive device connected to the piston, and a flow channel module detachably connected to the end of the extrusion cavity away from the casting cavity. The flow channel module has a converging flow channel connected to the extrusion chamber and a capillary flow channel connected to the converging flow channel.

2. The rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 1, characterized in that: The valve is a gate valve; The gate valve includes a valve body disposed on the outer wall of the material cylinder, a slide plate slidably disposed in the valve body and the material cylinder, and a drive rod connected to the slide plate; The axial direction of the feed cylinder is perpendicular to the plane where the insert plate is located.

3. The rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 1, characterized in that: The driving device includes a hydraulic press connected to the piston; the hydraulic press is used to drive the piston to move axially along the barrel.

4. The rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 1, characterized in that: The inner diameter of the converging channel near the extrusion chamber is the same as the inner diameter of the extrusion chamber, and the inner diameter of the converging channel near the capillary channel is the same as the inner diameter of the capillary channel.

5. The rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 4, characterized in that: The convergence angle of the convergent flow channel is 20-90 degrees; The diameter of the capillary channel is 2-6 mm, and the length-to-diameter ratio of the capillary channel is 10-40:

1.

6. The rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 5, characterized in that: It also includes a pressure detection system for detecting the pressure of the barrel and the flow channel module.

7. The rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 6, characterized in that: The pressure detection system includes a first pressure sensor disposed on the inner wall of the casting cavity, a second pressure sensor disposed at the inlet of the convergent flow channel, and a third pressure sensor disposed at the inlet of the capillary flow channel.

8. A testing method based on the rheological testing instrument for polytetrafluoroethylene paste extrusion as described in claim 7, characterized in that, Includes the following steps: (1) Close the valve and feed the slurry of polytetrafluoroethylene resin and lubricating oil into the casting cavity; (2) Using a drive device to push the piston with a constant pressure P, the slurry is squeezed and then held under pressure to form a bar blank; (3) Open the valve and use the drive device to drive the piston to push the billet into the extrusion chamber, and then continue to push it into the flow channel module; (4) Detect the pressure of the second pressure sensor through the pressure detection system. P 0 and the pressure of the third pressure sensor P 1; (5) Under the same barrel temperature and piston movement speed, replace the flow channel modules with different length-to-diameter ratios and repeat steps (3)-(4) to obtain multiple sets. P 0, P 1. Data; (6) Eliminate the inlet effect based on the collected data and use the Mooney method for wall slip correction to calculate the real rheological parameters.

9. The test method according to claim 8, characterized in that, The method for eliminating the entry effect in step (6) is as follows: Calculate the inlet pressure drop ΔP entry =P 0 P 1; Calculate the pressure drop in a pure capillary tube ΔP cap =P 1; Among them, the inlet pressure dropped ΔP entry Eliminated, using only pure capillary pressure drop ΔP cap Subsequent shear rheological calculations were then performed.

10. The test method according to claim 9, characterized in that, Step (6) of Mooney's method for wall slip correction specifically includes: according to the formula Calculate the apparent shear rate; According to the formula Calculate the apparent wall shear stress, where R is the capillary radius, L is the capillary length, and Q is the slurry volume flow rate; The apparent wall shear stress τ w,a Plotting a graph with 1 / R as the x-axis and performing a linear fit yields the fitted equation. Extrapolate to 1 / (L / R At point )=0, the true wall shear stress under no-slip condition is obtained. Combining volumetric flow rate, according to the formula The wall sliding velocity was calculated; In the formula, Q / (πR) 2 ) represents the average apparent velocity of the fluid within the capillary. true ×R / 3 is the average velocity caused by internal shearing of the fluid. The difference between the two is the relative slip velocity between the wall and the fluid. The larger the difference, the more significant the slip. Further according to the formula The actual shear rate is calculated; Finally, according to the formula To obtain the true viscosity.

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