CN117304550B - A high-strength waterproof polytetrafluoroethylene porous membrane and its preparation method and application - Google Patents

Abstract

The invention discloses a high-strength waterproof polytetrafluoroethylene porous membrane and its preparation method and application. The high-strength waterproof polytetrafluoroethylene porous membrane has a high-strength porous skeleton structure. The high-strength waterproof polytetrafluoroethylene porous membrane has a porous skeleton structure. The microscopic morphology of the porous membrane is a non-oriented rich and dense spider web-like structure, a thick "starfish" structure or a round hole structure. The high-strength waterproof polytetrafluoroethylene porous membrane has a high true waterproofing ability without a support. at 0.35MPa. The present invention changes the porous skeleton structure of the polytetrafluoroethylene porous membrane from the traditional point-like porous structure to a dense network structure, a high-strength starfish structure and a round hole structure, and the microscopic morphology of the membrane is no longer expanded. The structure improves the surface and internal density and strength of the membrane, making it difficult to delaminate, giving the membrane a high elastic modulus, high strength, small deformation, and easy recovery from deformation.

Description

A high-strength waterproof polytetrafluoroethylene porous membrane and its preparation method and application

Technical field

The present invention relates to the technical field of polymer porous membranes, and in particular to a high-strength waterproof polytetrafluoroethylene porous membrane and its preparation method and application.

Background technique

The existing polytetrafluoroethylene (PTFE) porous membrane production process mostly involves mixing PTFE dispersion resin with additives, pre-pressing and molding, push extrusion, calendering, removing additives, longitudinal stretching (MD) and transverse stretching. Stretching (TD), and then sintering and shaping. Due to the thermal sensitivity and creep properties of polytetrafluoroethylene materials, uneven stretching often occurs during the expansion process. The porous pore size distribution range is wide and the uniformity is poor. It is difficult to prepare small pores, and the thickness of different areas of the membrane varies greatly. At the same time, the porous morphology of the prepared membrane is an expanded network structure composed of "nodes-microfibers". Because the "microfibers" that constitute the porous structure of the membrane are too thin and weak, they are prone to deformation or breakage during use, causing the membrane to The pore size increases, and the protective ability and separation performance decrease. When the pore size is reduced through the stretching process, the porosity of the membrane decreases simultaneously, and the membrane is soft and thin, resulting in low mechanical strength of the membrane and easy deformation and scratching, which affects the performance. The expanded structure leads to low cohesion and easy delamination, which is not conducive to Subsequent processing.

Patent Publication Numbers CN201080002329.1 and CN201710063655.7, the invention discloses a waterproof sound-permeable membrane. The surface density of the PTFE porous membrane is 1-20g/m ^2. It adopts a multi-layer superposition and composite method, and is adhered by multi-layer stretching. The method controls the pore size of the membrane, and after stretching, it is fired at a temperature above the melting point of polytetrafluoroethylene to obtain a waterproof sound-permeable membrane.

Patent CN201880036006.0 uses high molecular weight polytetrafluoroethylene resin to push and mold, bake it into a non-porous membrane and then stretch it to adjust the number of pores in the membrane cross section and adjust the membrane pore size to improve its cohesion and puncture strength. The average pore diameter is in the range of 0.03 to 0.2 μm, and the porosity is greater than 25% and less than 90%.

Patent CN202080082140.1 obtains the molded product by selecting ultra-high molecular weight polytetrafluoroethylene, pre-pressing and extruding it, and stretching it in the extrusion direction at a molding temperature of 300°C at a certain speed. The porous membrane was fired at a temperature above the melting point of ethylene to prepare a small-pore size, high-strength polytetrafluoroethylene membrane. The bubble point under isopropyl alcohol is above 400kPa and the tensile strength is above 50MPa.

The above studies have regulated the pore size and strength of the membrane, but its porous structure has not changed. It is a single-layer or multi-layer composite expanded structure, composed of nodes and fibrils. The surface layer is loose, has poor mechanical strength, and is easy to deform. , scratches and delamination, membrane products have problems such as low mechanical strength, easy deformation and breakage of microfibers, and difficulty in maintaining the porous structure. During the waterproof capability test, due to the deformation problem caused by low strength, it is often necessary to set up a stainless steel wire mesh on the opposite side of the membrane's pressurized surface, and measure it in a state where deformation is suppressed, which is far from the actual application process.

Patent CN202010291100. By adding thermoplastic perfluoropolymer powder and performing a first high-temperature and short-time sintering process, the PTFE body is partially melted with a melting ratio of 0.5wt%-55wt% to create a new porous structure. The second sintering process achieves the tensile strength. By shaping and solidifying the porous structure of the post-porous body, the invention effectively improves the feel hardness or mechanical strength of the PTFE porous membrane. However, the porosity is low under small pore sizes, and adding powder can easily lead to uneven mixing and reduced product yield.

Therefore, how to adjust the microstructure of the membrane through process control, improve the mechanical strength of the membrane, change the problem of easy deformation and fracture, and produce a porous membrane with high strength, thin layer, small pore size, and high porosity to achieve waterproof and sound permeability The effect is a technical problem that needs to be solved urgently by those skilled in the art.

Contents of the invention

The purpose of the present invention is to provide a high-strength, truly waterproof polytetrafluoroethylene porous membrane in view of the poor mechanical strength of the polytetrafluoroethylene porous membrane in the prior art, which is prone to deformation and fracture.

Another object of the present invention is to provide a method for preparing the high-strength waterproof polytetrafluoroethylene porous membrane.

Another object of the present invention is to provide an application of the high-strength waterproof polytetrafluoroethylene porous membrane.

The technical solutions adopted to achieve the purpose of the present invention are:

A high-strength waterproof polytetrafluoroethylene porous membrane. The high-strength waterproof polytetrafluoroethylene porous membrane has a high-strength porous skeleton structure. The microscopic morphology of the high-strength waterproof polytetrafluoroethylene porous membrane is non-oriented. A rich and dense spider web-like structure, a thick "starfish" structure or a round hole structure. The spider web-like structure is a rich and dense network structure without nodes. The "starfish" structure is a thick microfibril in a divergent state. Adjacent island-shaped areas are connected, and the circular hole structure is a circular hole-like structure without nodes and obvious fiber structure;

The true waterproof capability of the high-strength waterproof polytetrafluoroethylene porous membrane without a support is not less than 0.35MPa.

In the above technical solution, the maximum pore size range of the high-strength waterproof polytetrafluoroethylene porous membrane is 20 nm-400 nm, the pore size distribution is more than 90%, and the thickness of the high-strength waterproof polytetrafluoroethylene porous membrane is 2 μm-70 μm.

In the above technical solution, the tensile breaking strength of the high-strength waterproof polytetrafluoroethylene porous membrane is 10 MPa-200 MPa, and the breaking elongation of the high-strength waterproof polytetrafluoroethylene porous membrane is less than 300%.

Another aspect of the invention provides a method for preparing the high-strength waterproof polytetrafluoroethylene porous membrane, which includes the following steps:

Step 1, mixing and pre-pressing molding: After mixing the dispersion resin and additive oil, the cylindrical or cylindrical PTFE rod blank is obtained by pre-pressing and molding;

Step 2, push and extrusion: push and extrude the rod blank obtained in step 1 through a horizontal or vertical push and extrusion equipment to obtain a rod-shaped or cylindrical PTFE parison;

Step 3, Calendering: Roll the rod-shaped or cylindrical PTFE parison obtained in Step 2 into a basic strip through a double-roller calender;

Step 4, degreasing treatment: heat the base material strip prepared in step 3 to remove additive oil;

Step 5, surface modification treatment: perform surface modification treatment on the base material strip after degreasing in step 4, apply the surface modification solution to the base material strip; then perform high temperature treatment, and then pass through a double-roller calender for two or more times Calendering is performed once to obtain the calendered base tape;

Step 6, longitudinal stretching: longitudinally stretch the calendered base tape after surface modification;

Step 7. Transverse stretching: The longitudinally stretched membrane sample is stretched transversely to obtain a PTFE body with a porous structure. The PTFE body with a porous structure is a high-strength waterproof polytetrafluoroethylene porous membrane.

In the above technical solution, the extrusion speed in step 2 is 40mm/min-200mm/min;

In the step 3, the roller diameter of the double-roller calender is 600mm-1000mm, and the thickness of the base material belt is 20μm-400μm;

The processing temperature of the degreasing treatment in step 4 is 150°C-280°C, and the processing time is 5min-30min.

In the above technical solution, the surface modification solution in step 5 includes 50%-80% polytetrafluoroethylene dispersion and 20%-50% aqueous polymer solution, and the concentration of the polytetrafluoroethylene dispersion is 30wt%-60wt%, the concentration of the aqueous polymer solution is 3wt%-10wt%, preferably, the aqueous polymer is polyvinyl alcohol PVA, polyacrylamide PAM, polyacrylic acid PAA, polyethylene oxide PEO or polyethylene oxide. One or more vinylpyrrolidone PVP;

The surface modification treatment method in step 5 is dipping, spraying, electrospinning coating or predetermined amount coating; the temperature of the high temperature furnace high temperature treatment in step 5 is 230°C-360°C. The thickness of the calendered base tape is 10μm-50μm.

In the above technical solution, the stretching temperature of longitudinal stretching in step 6 is 40°C-300°C, the stretching ratio is 50%-1000%, and the stretching distance is 20mm-200mm;

The stretching temperature of transverse stretching in step 7 is 20°C-300°C, the stretching ratio is 50%-2000%, and the stretching distance is 20mm-200mm.

The above technical solutions also include:

Step 8, sintering and shaping: The PTFE body with a porous structure obtained by stretching in step 7 is sintered and shaped while maintaining tension to obtain a high-strength waterproof polytetrafluoroethylene porous membrane.

In the above technical solution, the sintering temperature for sintering and shaping is 330°C-450°C, and the processing time for sintering and shaping is 0.5min-10min.

Another aspect of the present invention provides an application of the high-strength waterproof polytetrafluoroethylene porous membrane as a waterproof breathable membrane and a sound-permeable audio membrane in the field of consumer electronic products.

With the widespread use of electronic devices such as mobile phones, walkie-talkies, electronic watches, Bluetooth headsets, and outdoor monitors in daily life, in order to reduce the damage caused by water sports, outdoor environments, and daily water use to electronic devices, products of electronic devices are usually The microphone hole, balance vent and barometer vent that connect the inner cavity to the outside are equipped with waterproof breathable membranes for protection; for acoustic components such as speakers, microphones or earpieces, waterproof and sound-permeable audio membranes need to be used for isolation. For example, general sports watches or bracelets have higher requirements for the waterproof capabilities of waterproof, breathable and waterproof sound-permeable membranes. A 30-meter (0.3MPa) waterproof watch can be used for daily grooming or use in the rain, that is, water droplets only splash on the surface without Any water pressure is applied to the watch; the 50-meter waterproof watch can be used for swimming and general housework; the 100-meter waterproof watch can be used for underwater work such as swimming and diving. Waterproof performance is expressed by the numerical value of water pressure resistance test. For example, a membrane used in a 100-meter waterproof electronic device is required to have a water pressure resistance of 1 MPa. For a membrane to have a water pressure resistance of 1 MPa, its pore size needs to be several tens of nanometers or less. The high-strength waterproof polytetrafluoroethylene porous membrane of the present invention has a thin layer, high tensile strength, small elongation at break, and high waterproof ability, and is suitable for this purpose.

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

1. The high-strength waterproof polytetrafluoroethylene porous membrane of the present invention changes the porous skeleton structure of the membrane by modifying the surface layer of the base material tape, and then carries out high-temperature and low-magnification longitudinal stretching and medium-high-temperature and low-magnification transverse stretching. The point-like porous structure is transformed into a dense network structure, a high-strength starfish structure and a round hole structure, which improves the surface and internal density and strength of the membrane and is not easy to delaminate, making the membrane have a high elastic modulus, high strength and The deformation is small and the deformation is easy to recover. After stretching into a film, the sintering heat setting process does not need to be carried out, which simplifies the process and avoids the temperature gradient and stress release difference in the sintering setting process from affecting the film morphology, structure and pore size distribution, improves the uniformity and stability of the finished film, and effectively improves the The membrane surface and its porous skeleton structure have mechanical strength, deformation resistance and true waterproofing ability. The rich and dense porous structure makes the membrane not easy to deform, delaminate and scratch.

2. The high-strength waterproof polytetrafluoroethylene porous membrane of the present invention can avoid pressure deformation during application, maintain its own porous structure, and achieve high-strength true waterproofing capabilities.

Description of the drawings

Figure 1 is a flow chart of the preparation method of the high-strength waterproof polytetrafluoroethylene porous membrane of the present invention.

Figure 2 is a scanning electron microscope image of defatted base tape I.

Figure 3 is a scanning electron microscope image of the surface layer of the base tape corresponding to sample #1 after modification.

Figure 4 is a scanning electron microscope picture of sample 1#.

Figure 5 is a scanning electron microscope picture of sample 2#.

Figure 6 is a scanning electron microscope picture of sample 3#.

Figure 7 is a scanning electron microscope picture of sample 4#.

Figure 8 is a scanning electron microscope image of the PTFE base tape after surface modification treatment corresponding to sample 5#.

Figure 9 is a scanning electron microscope picture of sample 5#.

Figure 10 is the pore size distribution diagram of sample 5#, sample 6# and sample 7#.

Figure 11 is the scanning electron microscope picture of sample 6#.

Figure 12 is a scanning electron microscope picture of sample 7#.

Figure 13 is a scanning electron microscope image of sample #8.

Figure 14 is a scanning electron microscope picture of sample 9#.

Figure 15 is a scanning electron microscope picture of sample 10#.

Figure 16 is the pore size distribution diagram of the PTFE flat porous membrane of samples 8#, 9# and 10#.

Detailed ways

The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

The tensile breaking strength and breaking elongation of the high-strength waterproof polytetrafluoroethylene porous membrane of the present invention are tested using an electronic universal tensile machine (Instron 5965). The method refers to GB/T 1040.3-2006, the ambient temperature is 20°C, and the humidity 45% RH, sample width 20mm, stretching distance 150mm, stretching speed 150mm/min. The true waterproof capability is based on GB/T4208-2017. The effective test area is φ2mm. The test duration is one hour. There is no support, substrate or backboard in the effective test area. The porous morphology and structural characteristics of the membrane were characterized by a cryo-scanning electron microscope (HITACHIE S8200). The PTFE porous membrane was subjected to vacuum ion sputtering and gold spraying before testing. The pore size of the PTFE porous membrane is measured using a capillary flow pore size analyzer (POROMETERPOROLUX1000). The test method refers to CN 201510569827.9. The pore size distribution, maximum pore size, average pore size and minimum pore size are measured through the dry-wet curve using the principle of gas-liquid displacement. The stretching equipment is a high-temperature film biaxial stretching apparatus.

Example 1

A high-strength waterproof polytetrafluoroethylene porous membrane, as shown in Figure 1, is prepared by the following method:

Step 1, mixing and pre-pressing: Add 80 parts of Daikin's F104 dispersion resin to the mixing device, and mix evenly with 20 parts of ExxonMobil's Isopar G additive oil by spraying at 50 After aging for 24 hours under ℃ conditions, it is loaded into a φ150mm pre-pressing molding equipment, the pressure is set to 3.5MPa, and the pressure is maintained for 10 minutes to obtain a cylindrical PTFE rod blank.

Step 2, push extrusion: Push and extrude the rod blank through horizontal or vertical push extrusion equipment. The extrusion die size is φ15mm and the extrusion speed is 50mm/min to obtain a rod-shaped or cylindrical PTFE parison.

Step 3, Calendering: Roll the rod-shaped or cylindrical PTFE parison into a basic material strip through a double-roller calender with a roller diameter of 600mm. The rolling speed is 20m/min (the rolling speed is used in subsequent embodiments of the present invention). ), the base strip thickness is 60μm.

Step 4, degreasing treatment: The basic material tape prepared in step 3 is sent to a high-temperature oven for heating treatment to remove the additive oil in the mold body. The processing temperature is 230°C and the processing time is 30 minutes to obtain degreasing base tape Ⅰ and degreasing base tape Ⅰ. The micromorphology is shown in Figure 2.

Steps 5-8, surface modification treatment, longitudinal stretching, transverse stretching, sintering and shaping:

Sample 1#: Surface modification of the base tape is achieved by surface modification of the defatted base tape I. The surface modification solution is coated on the base material belt through electrospinning, and is treated at high temperature in a high-temperature furnace; then passed through a double-roller calender for secondary rolling to obtain a calendered base belt with a thickness of 50 μm. The surface modification solution includes 50% polytetrafluoroethylene dispersion and 50% PVP solution. The concentration of the polytetrafluoroethylene dispersion is 60wt% and the concentration of the PVP solution is 5wt. %; the temperature of the high temperature treatment is 260°C. The micromorphology of the surface-modified base tape is shown in Figure 3. The film biaxial stretching equipment is used to stretch the basic material tape after surface modification in the longitudinal direction. The stretching temperature is 250°C, the stretching ratio is 800%, and the stretching spacing is 150mm. The film sample after longitudinal stretching is stretched transversely. , the stretching temperature is 40°C, the stretching ratio is 200%, the stretched PTFE body with a porous structure is sintered and shaped under the action of maintaining tension, the sintering temperature is 330°C, the processing time is 5 minutes, and a high-strength PTFE body with a thickness of 37 μm is obtained. Waterproof polytetrafluoroethylene porous membrane sample 1#.

Sample 2#: Surface modification of the base tape is achieved by surface modification of the defatted base tape I. The surface modification solution is coated on the base material belt through electrospinning and treated at high temperature in a high-temperature furnace; the surface modification solution includes 60% polytetrafluoroethylene dispersion and 40% PVP solution, the concentration of the polytetrafluoroethylene dispersion is 60wt%, and the concentration of the PVP solution is 5wt%; the temperature of the high-temperature treatment is 270°C, the film thickness after secondary calendering is 50 μm, and other baseband processing conditions are the same as sample 1# same. Use film biaxial stretching equipment to stretch the basic material tape after surface modification. First, perform longitudinal stretching at a stretching temperature of 250°C, a stretching ratio of 800%, and a stretching spacing of 150mm; for the longitudinally stretched film sample Carry out transverse stretching at a stretching temperature of 40°C, a stretching ratio of 400%, and a stretching distance of 150mm. The stretched PTFE body with a porous structure is sintered and shaped while maintaining tension. The sintering temperature is 330°C and the processing time is 330°C. After 10 minutes, a high-strength waterproof polytetrafluoroethylene porous membrane sample 2# with a thickness of 40 μm was obtained.

Sample 3#: adopt the same treatment method as sample 1#, the surface modification solution includes 70% polytetrafluoroethylene dispersion and 30% PVA solution, the polytetrafluoroethylene The concentration of the dispersion liquid is 60wt%, the concentration of the PVA solution is 4wt%, the high temperature is 280°C, and the film thickness after secondary calendering is 50 μm. Use film biaxial stretching equipment to longitudinally stretch the basic material tape after surface modification. The stretching temperature is 250°C, the stretching ratio is 1000%, the stretching spacing is 150mm, and the stretching rate is 150mm/min; after longitudinal stretching, The film sample was stretched transversely at a stretching temperature of 40°C, a stretching ratio of 200%, a stretching spacing of 150mm, and a stretching rate of 150mm/min. The PTFE body with a porous structure obtained by stretching was stretched while maintaining tension. After sintering and shaping, the sintering temperature is 335°C and the processing time is 10 minutes, and a high-strength waterproof polytetrafluoroethylene porous membrane sample 3# with a thickness of 35 μm is obtained.

Sample 4#: adopt the same treatment method as sample 1#, the surface modification solution includes 80% polytetrafluoroethylene dispersion and 20% PVA solution, the polytetrafluoroethylene The concentration of the dispersion liquid is 60wt%, the concentration of the PVA solution is 3wt%, the high temperature is 300°C, and the film thickness after secondary calendering is 50 μm. Use film biaxial stretching equipment to longitudinally stretch the basic material tape after surface modification. The stretching temperature is 250°C, the stretching ratio is 600%, the stretching spacing is 150mm, and the stretching rate is 150mm/min; after longitudinal stretching, The film sample was stretched transversely at a stretching temperature of 60°C, a stretching ratio of 300%, a stretching spacing of 150mm, and a stretching rate of 150mm/min. The PTFE body with a porous structure obtained by stretching was stretched while maintaining tension. After sintering and shaping, the sintering temperature is 335°C and the processing time is 5 minutes, and a high-strength waterproof polytetrafluoroethylene porous membrane sample 4# with a thickness of 38 μm is obtained.

The morphology and structure of the high-strength waterproof polytetrafluoroethylene porous membrane prepared from Sample 1# to Sample 4# are shown in Figures 4-7 respectively. The porous structure is a spider-like structure with thick fibers and no obvious nodes and orientation. The test data of sample 1#-sample 4# are detailed in Table 1.

Comparing the morphology of the defatted base tape (Figure 2) with the morphology of the base tape after surface modification in Example 1 (Figure 3), it can be found that the defatted base tape exhibits a loose structure with microscopic particles arranged in an orderly manner. After coating, high-temperature treatment and secondary calendering, the surface modification liquid and the polytetrafluoroethylene dispersion resin are integrated into the base tape. After secondary calendering, the overall structure of the base tape has smaller pores and is more dense, which is beneficial to improving the surface strength of the membrane. And can form a high-strength multi-layered skeleton structure. The structural morphology of the film in Example 1 of the present invention is as shown in Figure 4-7. After the surface layer modification treatment of the base tape, after longitudinal stretching (MD), transverse stretching (TD) and sintering and shaping, the prepared film has rich, Multi-layered, nodeless spider web-like structure, the fibers are thick and have no obvious directionality, the pore size is small, the longitudinal tensile strength and transverse tensile strength are higher, the film thickness is about 30-40 μm, and the film's true waterproof ability is Reaching more than 0.35MPa.

Compared with the present invention, the membrane structures produced by the existing stretching technology are mostly fibrous expanded structures, which are difficult to prepare small pore structures; the fibers are thin, have poor mechanical strength, large elongation at break, weak resistance to deformation, and are easy to deform. , it is difficult to withstand the deformation and damage of the membrane caused by the impact of high-pressure liquid.

Table 1 Various test data of sample 1#-sample 4#

Example 2

A high-strength waterproof polytetrafluoroethylene porous membrane is prepared by the following method:

Step 1: Add 79 parts of Daikin's F104 dispersion resin to the mixing device, mix 21 parts of ExxonMobil's Isopar M additive oil evenly by spraying, and mature it at 50°C for 24 hours. Fill it into a φ130mm pre-pressing molding equipment, set the pressure to 3.5MPa, and maintain the pressure for 10 minutes to obtain a cylindrical PTFE rod blank.

Step 2: Push and extrude the rod blank through horizontal or vertical push extrusion equipment. The extrusion die size is φ17.5mm and the extrusion speed is 100mm/min to obtain a rod-shaped or cylindrical PTFE parison;

Step 3: Roll the rod-shaped or cylindrical PTFE parison into a basic material strip through a double-roller calender with a roller diameter of 800mm. The thickness of the basic material strip is 50 μm. The thickness is measured using an infrared online analysis thickness sensor.

Step 4: Heat the above-mentioned base material tape to remove the additive oil in the mold body. The treatment temperature is 260°C and the treatment time is 30 minutes to obtain the degreasing base tape II.

Step 5: Modify the surface of the base tape by performing surface modification treatment on the defatted base tape II. The surface modification solution is sprayed on the base material belt through high-pressure air gun spraying, and is treated at high temperature in a high-temperature furnace; then passed through a double-roller calender for secondary rolling to obtain a calendered base belt with a thickness of 30 μm. The surface modification solution includes a polytetrafluoroethylene dispersion with a proportion of 60% and a PVA solution with a proportion of 40%. The concentration of the polytetrafluoroethylene dispersion is 60wt%, and the concentration of the PVA solution is 3wt%. ; The temperature of the high temperature treatment is 330°C. The micromorphology of the surface-modified base tape is shown in Figure 8. There are no obvious resin particles on the surface of the base tape, and the secondary resin particles are integrated into one body. The gaps within the field of view of the base tape surface are further reduced;

Step 6: First stretch the basic material tape after surface modification in the longitudinal direction at a stretching temperature of 260°C, a stretching ratio of 200%, and a stretching distance of 100mm;

Step 7: Stretch the longitudinally stretched membrane sample transversely at a stretching temperature of 200°C, a stretching ratio of 300%, and a stretching spacing of 100mm to obtain a high-strength waterproof polytetrafluoroethylene porous membrane sample 5# with a thickness of 35 μm. .

The average pore size and pore size distribution of the prepared PTFE flat plate porous membrane were tested. The pore size distribution results of sample 5# are shown in Figure 10. The morphology and structure of sample 5# is shown in Figure 9. The concentration of the surface modification treatment liquid increases, the high-temperature treatment temperature increases, and the porous structure of the membrane takes on a starfish-like structure. The test data of sample 5# are detailed in Table 2.

Example 3

Step 1: Add 79 parts of Daikin's F106 dispersion resin to the mixing device, mix 21 parts of ExxonMobil's Isopar M additive oil evenly by spraying, and mature it at 50°C for 24 hours. Fill it into a φ150mm pre-pressing molding equipment, set the pressure to 3.5MPa, and maintain the pressure for 10 minutes to obtain a cylindrical PTFE rod blank.

Step 2: Push and extrude the rod blank through horizontal or vertical push extrusion equipment. The extrusion die size is φ15mm and the extrusion speed is 100mm/min to obtain a rod-shaped or cylindrical PTFE parison;

Step 3: Roll the rod-shaped or cylindrical PTFE parison into a basic material strip through a double-roller calender with a roller diameter of 800mm. The thickness of the basic material strip is 40 μm. The thickness is measured using an infrared online analysis thickness sensor.

Step 4: Heat the above-mentioned base material tape to remove the additive oil in the mold body. The treatment temperature is 260°C and the treatment time is 30 minutes to obtain the degreasing base tape III.

Steps 5-7:

Sample 6#: Step 5: Surface modification of the base tape is achieved by surface modification of the degreasing base tape III. The surface modification solution is evenly sprayed on the base material tape through a predetermined amount of coating, and is treated at high temperature in a high-temperature furnace; and then passed through double rollers. The calender is used for secondary calendering to obtain a calendered base tape with a thickness of 30 μm. The surface modification solution includes a polytetrafluoroethylene dispersion with a proportion of 40% and a PVA solution with a proportion of 60%. The concentration of the polytetrafluoroethylene dispersion is 60wt%, and the aqueous polymer solution concentration is 3wt%; the temperature of the high temperature treatment is 335°C;

Step 6: First stretch the basic material tape after surface modification in the longitudinal direction at a stretching temperature of 260°C, a stretching ratio of 200%, and a stretching distance of 100mm;

Step 7: Stretch the longitudinally stretched membrane sample transversely at a stretching temperature of 230°C, a stretching ratio of 200%, and a stretching spacing of 100mm to obtain a high-strength waterproof polytetrafluoroethylene porous membrane sample #6 with a thickness of 25 μm. .

Sample 7#: Step 5: Surface modification of the base tape is achieved by surface modification of the degreasing base tape III. The surface modification solution is evenly sprayed on the base material tape by dipping, and is treated at high temperature in a high-temperature furnace; and then passed through a double-roller calender. Perform secondary rolling to obtain a base tape thickness of 30 μm. The surface modification solution includes a polytetrafluoroethylene dispersion with a proportion of 60% and a PVA solution with a proportion of 40%. The concentration of the polytetrafluoroethylene dispersion is 60wt%, and the aqueous polymer solution concentration is 3wt%; the high temperature is 340℃;

Step 6: First stretch the basic material tape after surface modification in the longitudinal direction at a stretching temperature of 260°C, a stretching ratio of 200%, and a stretching distance of 100mm;

Step 7: Stretch the longitudinally stretched membrane sample transversely at a stretching temperature of 260°C, a stretching ratio of 200%, and a stretching spacing of 100mm to obtain a high-strength waterproof polytetrafluoroethylene porous membrane sample 7# with a thickness of 17 μm. .

The average pore size and pore size distribution of sample 6# and sample 7# were tested. The pore size distribution results are shown in Figure 10. The morphology and structure of samples 6# and 7# are shown in Figures 11 and 12. The porous structure is characterized by a unique round hole structure with no node fiber structure. The test data of sample 6# and sample 7# are detailed in Table 2.

Comparing the morphology of the degreasing base tape (Figure 2) and the morphology of the base tape after surface modification in Example 2 (Figure 8), it can be seen that the surface modification liquid in Example 2 adopts a spraying method, and the coating is more uniform; the surface layer above the melting point of the material After high-temperature treatment, the surface modification liquid and resin are melted into one body, gradually moving from the loose resin particle state to a dense surface state without obvious gaps; the second calendering to a thinner thickness orients the modified layer twice, which also makes the modified layer and the base tape The bonding between them is tighter, the molecular chains are entangled and cross-linked together, and the degree of freedom of molecular movement is reduced. Therefore, a high-strength starfish-like pore structure is formed after biaxial stretching, as shown in Figure 9. The thick microfibrils diverge in an unoriented manner. The state is connected to the adjacent island area, and the average pore diameter is further reduced to 115.9 nm, which increases the mechanical strength (longitudinal tensile strength reaches 39.2 MPa and transverse tensile strength reaches 11.5 MPa), and the true waterproof ability of the membrane increases to 1.0MPa.

Example 3 further uses a higher concentration of surface modification liquid and processing temperature, and is calendered to a thinner thickness of 30 μm. The volume density of the base tape is further increased. After biaxial stretching, the thickness of the film can be as thin as 17 μm. The morphology and structure of the film , as shown in Figure 11-12, has a unique fiber-free round hole structure. The holes are no longer connected by fibers, but are connected "island-island". The average pore diameter is further reduced to 66.7nm, mechanically It has higher strength (longitudinal tensile strength reaches 70.2 MPa, transverse tensile strength reaches 50.5 MPa), tensile strength and waterproof ability are simultaneously improved, and true waterproof ability is increased to 1.5 MPa.

On the other hand, in order to eliminate the internal stress during the stretching process, the existing technology requires sintering and shaping. This process will broaden the pore size distribution of the membrane and is not conducive to the concentration of pore size distribution and the uniformity of the membrane. In Examples 2 and 3 of the present invention, after surface modification treatment and biaxial stretching to form a film, there is no need to perform a sintering and shaping step. The surface modification treatment can be seen from the morphology and structure of the film in Figures 9, 11 and 12. The post-stretched membrane has a regular pore structure, concentrated pore size distribution, high mechanical strength, and strong true waterproof ability.

Table 2 Various test data of sample 5#-sample 7#

Comparative example 1

By biaxially stretching the degreasing base tape I, first perform longitudinal stretching at a stretching temperature of 250°C, a stretching ratio of 500%, and a stretching spacing of 150mm; the film sample after longitudinal stretching is stretched transversely at a stretching temperature of 250°C. ℃, the stretching ratio is 500%, and the stretching spacing is 100mm, to obtain PTFE flat porous membrane sample #8 with a thickness of 30 μm.

Comparative example 2

By biaxially stretching the degreasing base tape I, first perform longitudinal stretching at a stretching temperature of 250°C, a stretching ratio of 250%, and a stretching spacing of 150mm; the film sample after longitudinal stretching is stretched transversely at a stretching temperature of 250°C. ℃, stretching ratio 200%, stretching distance 150mm, and obtained PTFE flat porous membrane sample 9# with a thickness of 35μm.

Comparative example 3

By biaxially stretching the degreasing base tape III, first perform longitudinal stretching at a stretching temperature of 250°C, a stretching ratio of 250%, and a stretching spacing of 150mm; the film sample after longitudinal stretching is stretched transversely at a stretching temperature of 250°C. ℃, stretching ratio 400%, stretching distance 100mm, and obtained PTFE flat porous membrane sample 10# with a thickness of 37 μm.

Comparative example 4

The surface modification liquid is cast onto the glass plate, and after high-temperature treatment in a high-temperature furnace, the formed polytetrafluoroethylene strip is separated from the glass plate. The surface modification solution includes a polytetrafluoroethylene dispersion with a proportion of 60% and a PVA solution with a proportion of 40%. The concentration of the polytetrafluoroethylene dispersion is 60wt%, and the aqueous polymer solution concentration is 3wt%, the temperature of the high temperature treatment is 330°C. When the polytetrafluoroethylene tape was stretched, the tape broke and could not be stretched into a film.

Scanning electron microscopy and pore size distribution of the prepared PTFE flat plate porous membranes were tested. The morphology and structure of the PTFE flat plate porous membranes prepared from samples 8#, 9# and 10# are shown in Figures 13, 14 and 15. The porous structure is characterized by a loose structure. Expanded fiber structure; pore size distribution results are shown in Figure 16. The test data of sample 8#-sample 10# are detailed in Table 3.

Table 3 Various test data of samples 8#-10# in comparative examples 1-3

Comparing the morphology of the defatted base tape (Figure 2) and the morphology of the base tape after surface modification (Figure 3, Figure 8), it can be seen that the defatted base tape resin is in the form of granular and tightly arranged secondary particles, as shown in Comparative Example 1 The morphology structure of the obtained film is an expanded structure of "small nodes and fine fibers". The morphology of the film after stretching in Comparative Example 2 is an expanded structure of "large nodes-fibers". The morphology of the film in Comparative Example 3 is an expanded structure of "large nodes-fibers". Comparative Example 3 has directional fiber nodes. shape structure. Comparative Example 4 cannot be stretched into a film because the strength of the material belt is too low.

Comparing the micromorphology diagrams of Sample 1# to Sample 4# in the Comparative Example and Example 1, it can be found that as the concentration of the polytetrafluoroethylene aqueous dispersion in the surface modification solution increases, the PTFE prepared by biaxial stretching becomes porous. The membrane has a rich network structure with thick, rich and dense fibers. In Examples 2 and 3, the concentration of the aqueous dispersion of polytetrafluoroethylene in the surface modification solution and the high-temperature treatment temperature were further increased, and after the secondary calendering process, the surface layer of the base tape showed a dense structure without voids after the surface modification treatment. Sample 5 The microscopic morphology of # is a high-strength starfish shape. The starfish-like structure is composed of thick microfibrils connected to adjacent island-like areas in a divergent state, and the fibers present a multi-layered interlaced structure; samples 6# and 7# are evenly arranged. The round hole structure of the cloth is a round hole-like structure with no nodes and no obvious fiber structure. It can be seen from the tensile strength test results that the starfish-shaped structure and the round hole structure have higher mechanical strength and smaller elongation at break.

The above are only preferred embodiments of the present invention. It should be noted that those skilled in the art can also make several improvements and modifications without departing from the principles of the present invention. These improvements and Retouching should also be considered within the scope of the present invention.

Claims (10)

1. A high-strength waterproof polytetrafluoroethylene porous membrane, characterized in that the high-strength waterproof polytetrafluoroethylene porous membrane has a high-strength porous skeleton structure, and the microscopic structure of the high-strength waterproof polytetrafluoroethylene porous membrane is The morphology is a non-oriented rich and dense spider web-like structure, a thick "starfish" structure or a round hole structure. The spider web-like structure is a rich and dense network structure without nodes, and the "starfish" structure is a thick microscopic structure. The fibrils are connected to adjacent island-shaped areas in a divergent state, and the round hole structure is a round hole structure without nodes and obvious fiber structure; The true waterproofing capacity of the high-strength waterproof polytetrafluoroethylene porous membrane without a support is not less than 0.35MPa, The high-strength waterproof polytetrafluoroethylene porous membrane is prepared by the following method: Step 1, mixing and pre-pressing molding: After mixing the dispersion resin and additive oil, the cylindrical or cylindrical PTFE rod blank is obtained by pre-pressing and molding; Step 2, push and extrusion: push and extrude the rod blank obtained in step 1 through a horizontal or vertical push and extrusion equipment to obtain a rod-shaped or cylindrical PTFE parison; Step 3, Calendering: Roll the rod-shaped or cylindrical PTFE parison obtained in Step 2 into a basic strip through a double-roller calender; Step 4, degreasing treatment: heat the base material strip prepared in step 3 to remove additive oil; Step 5, surface modification treatment: perform surface modification treatment on the base material strip after degreasing in step 4, apply the surface modification solution to the base material strip; then perform high temperature treatment, and then pass through a double-roller calender for two or more times Calendering is performed once to obtain the calendered base tape; Step 6, longitudinal stretching: longitudinally stretch the calendered base tape after surface modification; Step 7, transverse stretching: Stretch the longitudinally stretched membrane sample transversely to obtain a PTFE body with a porous structure. The PTFE body with a porous structure is a high-strength waterproof polytetrafluoroethylene porous membrane; Wherein, the surface modification solution in step 5 includes 50%-80% polytetrafluoroethylene dispersion and 20%-50% aqueous polymer solution, and the concentration of the polytetrafluoroethylene dispersion is 30wt%-60wt %, the concentration of the aqueous polymer solution is 3wt%-10wt%, the aqueous polymer is one of polyvinyl alcohol PVA, polyacrylamide PAM, polyacrylic acid PAA, polyethylene oxide PEO or polyvinylpyrrolidone PVP or more. 2. The high-strength waterproof polytetrafluoroethylene porous membrane as claimed in claim 1, characterized in that the maximum pore size range of the high-strength waterproof polytetrafluoroethylene porous membrane is 20 nm-400 nm, and the high-strength waterproof polytetrafluoroethylene porous membrane The thickness of the PTFE porous membrane is 2 μm-70 μm. 3. The high-strength waterproof polytetrafluoroethylene porous membrane as claimed in claim 1, wherein the tensile breaking strength of the high-strength waterproof polytetrafluoroethylene porous membrane is 10 MPa-200 MPa, and the high The elongation at break of the strong waterproof polytetrafluoroethylene porous membrane is less than 300%. 4. A method for preparing the high-strength waterproof polytetrafluoroethylene porous membrane according to any one of claims 1 to 3, characterized in that it includes the following steps: Step 1, mixing and pre-pressing molding: After mixing the dispersion resin and additive oil, the cylindrical or cylindrical PTFE rod blank is obtained by pre-pressing and molding; Step 2, push and extrusion: push and extrude the rod blank obtained in step 1 through a horizontal or vertical push and extrusion equipment to obtain a rod-shaped or cylindrical PTFE parison; Step 3, Calendering: Roll the rod-shaped or cylindrical PTFE parison obtained in Step 2 into a basic strip through a double-roller calender; Step 4, degreasing treatment: heat the base material strip prepared in step 3 to remove additive oil; Step 5, surface modification treatment: perform surface modification treatment on the base material strip after degreasing in step 4, apply the surface modification solution to the base material strip; then perform high temperature treatment, and then pass through a double-roller calender for two or more times Calendering is performed once to obtain the calendered base tape; Step 6, longitudinal stretching: longitudinally stretch the calendered base tape after surface modification; Step 7. Transverse stretching: The longitudinally stretched membrane sample is stretched transversely to obtain a PTFE body with a porous structure. The PTFE body with a porous structure is a high-strength waterproof polytetrafluoroethylene porous membrane. 5. The preparation method according to claim 4, characterized in that the extrusion speed in step 2 is 40mm/min-200mm/min; In the step 3, the roller diameter of the double-roller calender is 600mm-1000mm, and the thickness of the base material belt is 20μm-400μm; The processing temperature of the degreasing treatment in step 4 is 150°C-280°C, and the processing time is 5min-30min. 6. The preparation method according to claim 4, wherein the surface modification treatment in step 5 is dipping, spraying, electrospinning coating or predetermined amount coating; the high temperature treatment in step 5 The temperature is 230°C-360°C, and the thickness of the calendered base tape is 10 μm-50 μm. 7. The preparation method according to claim 4, characterized in that the stretching temperature of longitudinal stretching in step 6 is 40°C-300°C, the stretching ratio is 50%-1000%, and the stretching distance is 20mm. -200mm; The stretching temperature of transverse stretching in step 7 is 20°C-300°C, the stretching ratio is 50%-2000%, and the stretching distance is 20mm-200mm. 8. The preparation method according to claim 4, further comprising: Step 8, sintering and shaping: The PTFE body with a porous structure obtained by stretching in step 7 is sintered and shaped while maintaining tension to obtain a high-strength waterproof polytetrafluoroethylene porous membrane. 9. The preparation method according to claim 8, wherein the sintering temperature for sintering and shaping is 330°C-450°C, and the processing time for sintering and shaping is 0.5min-10min. 10. Application of the high-strength waterproof polytetrafluoroethylene porous membrane according to any one of claims 1 to 3 as a waterproof breathable membrane and sound-transparent audio membrane in the field of consumer electronic products.