Ultra-thick perfluorinated microporous membranes, process for their preparation and use thereof

Abstract

The application discloses an ultra-thick perfluorinated microporous membrane, a preparation process and application thereof, relates to the technical field of microporous membranes, and comprises a first PTFE microporous membrane, a first PVDF microporous adhesive layer, a second PTFE microporous membrane, a second PVDF microporous adhesive layer and a third PTFE microporous membrane arranged in sequence from bottom to top; the first PVDF microporous adhesive layer is embedded into surface membrane holes of the first PTFE microporous membrane and the second PTFE microporous membrane; and the second PVDF microporous adhesive layer is embedded into surface membrane holes of the second PTFE microporous membrane and the third PTFE microporous membrane, beneficial effects are as follows: PVDF is used as a microporous adhesive layer, when heat treatment is carried out, the temperature only needs to reach 170 DEG C to 185 DEG C, so that the three-layer PTFE microporous membrane can be bonded, the porosity and the pore size of the three-layer PTFE microporous membrane remain basically unchanged in the temperature interval, meanwhile, the micropores of the first PVDF microporous adhesive layer and the PVDF microporous adhesive layer are controlled to be open sponge-like micropores and the pore size is greater than that of the three-layer PTFE microporous membrane, so that the use environment of the diaphragm of the super tantalum capacitor is met.

Description

Technical Field

[0001] This invention relates to the field of microporous membrane technology, and in particular to an ultra-thick perfluorinated microporous membrane, its preparation process, and its applications. Background Technology

[0002] The diaphragm of a super tantalum capacitor is in a strong acid and high temperature environment, such as the sulfuric acid concentration in the electrolyte can reach 20%-50%, and the temperature can reach 100℃-150℃, and the thickness of the diaphragm is required to be high.

[0003] Currently, ultra-thick perfluorinated microporous membranes are formed through one-time stretching or heat treatment of multilayer microporous membranes. However, in one-time stretching, although the membrane thickness is increased, the thickness and pore uniformity are insufficient, and the thermal shrinkage rate is high, making it difficult to meet the actual application requirements. In the heat treatment process of multilayer microporous membranes, if the heat treatment temperature is too high, the pore morphology of the microporous membrane will be destroyed, resulting in partial closure of the ultra-thick perfluorinated microporous membrane or a large change in pore size. This leads to poor transmission channels or insufficient retention capacity of the ultra-thick perfluorinated microporous membrane, which also makes it difficult to meet the actual application requirements.

[0004] Therefore, there is an urgent need to develop an ultra-thick perfluorinated microporous membrane, its preparation process, and its applications to overcome the aforementioned defects. Summary of the Invention

[0005] The purpose of this invention is to disclose an ultra-thick perfluorinated microporous membrane, its preparation process, and its applications.

[0006] The first objective of this invention is to develop an ultra-thick perfluorinated microporous membrane.

[0007] The second objective of this invention is to develop applications for an ultra-thick perfluorinated microporous membrane.

[0008] The third objective of this invention is to develop a process for preparing ultra-thick perfluorinated microporous membranes.

[0009] To achieve the first objective mentioned above, the present invention provides an ultra-thick perfluorinated microporous membrane, comprising, from bottom to top, a first PTFE microporous membrane, a first PVDF microporous adhesive layer, a second PTFE microporous membrane, a second PVDF microporous adhesive layer, and a third PTFE microporous membrane.

[0010] The thicknesses of the first PTFE microporous membrane, the second PTFE microporous membrane, and the third PTFE microporous membrane are 30 μm-70 μm, respectively;

[0011] The first PVDF microporous adhesive layer is located between the first PTFE microporous membrane and the second PTFE microporous membrane and is embedded in the surface pores of the first PTFE microporous membrane and the second PTFE microporous membrane;

[0012] The second PVDF microporous adhesive layer is located between the second PTFE microporous membrane and the third PTFE microporous membrane and is embedded in the surface pores of the second PTFE microporous membrane and the third PTFE microporous membrane.

[0013] Preferably, the porosity of the first PTFE microporous membrane, the second PTFE microporous membrane, and the third PTFE microporous membrane are 50%-90%, and the pore size is 0.03μm-1.0μm, respectively.

[0014] Preferably, the pore sizes of the first PVDF microporous adhesive layer and the second PVDF microporous adhesive layer are larger than the pore sizes of the first PTFE microporous membrane, the second PTFE microporous membrane, and the third PTFE microporous membrane.

[0015] Preferably, the ultra-thick perfluorinated microporous membrane has a porosity of 50%-85%, a pore size of 0.03μm-1.0μm, and a thickness of 85μm-210μm.

[0016] Preferably, the micropores of the first PVDF microporous adhesive layer and the second PVDF microporous adhesive layer are open, sponge-like micropores.

[0017] Based on the same inventive principle, in order to achieve the second inventive objective mentioned above, the present invention provides an application in which the ultra-thick perfluorinated microporous membrane described in the first invention is used as a separator for a super tantalum capacitor.

[0018] Based on the same inventive principle, and to achieve the third inventive objective mentioned above, this invention provides a process for preparing an ultra-thick perfluorinated microporous membrane, comprising the following steps:

[0019] Step S1: Prepare a first PTFE microporous membrane, a second PTFE microporous membrane, and a third PTFE microporous membrane with a thickness of 30μm-70μm by a stretching process;

[0020] Step S2: Prepare PVDF adhesive solution;

[0021] Step S3: Immerse the second PTFE microporous membrane in the PVDF adhesive solution from step S2 to obtain an impregnated membrane;

[0022] Step S4: The first PTFE microporous membrane, the impregnated membrane, and the third PTFE microporous membrane are successively processed through a composite process, a phase transformation process, and a heat treatment process to form the ultra-thick perfluorinated microporous membrane described in the first invention.

[0023] Preferably, the method includes the following steps: the porosity of the first PTFE microporous membrane, the second PTFE microporous membrane, and the third PTFE microporous membrane are 50%-90%, and the pore size is 0.03μm-1.0μm, respectively.

[0024] Preferably, in step S3, the amount of PVDF adhesive is measured using a scraper.

[0025] Preferably, the preparation process for the PVDF adhesive is as follows:

[0026] Choose a single solvent or a mixed solvent, add PVDF polymer to the solvent and stir thoroughly to form a PVDF adhesive solution, with a PVDF content of 0.5%-5%;

[0027] The surface tension of the solvent is less than or equal to the surface tension of PVDF.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] PTFE has a melting point of 327℃, while PVDF has a melting point between 165℃ and 175℃. Using PVDF as a microporous adhesive layer, three layers of PTFE microporous membrane are bonded together. During heat treatment, the temperature only needs to reach between 170℃ and 185℃ to bond the three layers of PTFE microporous membrane. Within this temperature range, the porosity and pore size of the first, second, and third PTFE microporous membranes remain essentially unchanged. At the same time, through a phase inversion process, the micropores of the first and second PVDF microporous adhesive layers are controlled to be open, sponge-like micropores with a pore size larger than that of the three PTFE microporous membranes. This ensures that the pore size of the composite ultra-thick perfluorinated microporous membrane remains essentially unchanged. Given the acid resistance, oxidation resistance, and high temperature resistance of PTFE and PVDF, the membrane meets the usage environment requirements of super tantalum capacitors. Attached Figure Description

[0030] Figure 1 This is a cross-sectional schematic diagram of the ultra-thick perfluorinated microporous membrane of the present invention.

[0031] Figure 2 This is a flowchart illustrating the process for preparing the ultra-thick perfluorinated microporous membrane of this invention.

[0032] Among them, 1. First PTFE microporous membrane; 2. First PVDF microporous adhesive layer; 3. Second PTFE microporous membrane; 4. Second PVDF microporous adhesive layer; 5. Third PTFE microporous membrane. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0034] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0035] The specific implementation process of the present invention will be described below through several embodiments.

[0036] Example 1:

[0037] See Figure 1 This embodiment discloses an ultra-thick perfluorinated microporous membrane, comprising, from bottom to top, a first PTFE microporous membrane 1, a first PVDF microporous adhesive layer 2, a second PTFE microporous membrane 3, a second PVDF microporous adhesive layer 4, and a third PTFE microporous membrane 5; the thicknesses of the first PTFE microporous membrane 1, the second PTFE microporous membrane 3, and the third PTFE microporous membrane 5 are 30μm-70μm, respectively; the first PVDF microporous adhesive layer 2 is located between the first PTFE microporous membrane 1 and the second PTFE microporous membrane 3 and is embedded in the surface pores of the first PTFE microporous membrane 1 and the second PTFE microporous membrane 3; the second PVDF microporous adhesive layer 4 is located between the second PTFE microporous membrane 3 and the third PTFE microporous membrane 5 and is embedded in the surface pores of the second PTFE microporous membrane 3 and the third PTFE microporous membrane 5.

[0038] Specifically, currently, ultra-thick perfluorinated microporous membranes are formed through one-time stretching or heat treatment of multilayer PTFE microporous membranes. One-time stretching suffers from excessively high porosity and insufficient uniformity. For multilayer PTFE microporous membranes, the heat treatment temperature must reach the point where PTFE melts to achieve adhesion between layers, but this results in excessively high heat treatment temperatures that damage the pore structure. Therefore, this embodiment uses PVDF as the microporous adhesive layer. PVDF has a melting point between 165°C and 175°C, which is much lower than the melting point of PTFE (327°C). See [link to relevant documentation]. Figure 1To heat-treat and bond the first PTFE microporous membrane 1, the first PVDF microporous adhesive layer 2, the second PTFE microporous membrane 3, the second PVDF microporous adhesive layer 4, and the third PTFE microporous membrane 5 together, the heat treatment temperature only needs to reach between 170℃ and 185℃. The adhesive effect of PVDF will then bond the first PTFE microporous membrane 1, the second PTFE microporous membrane 3, and the third PTFE microporous membrane 5 together. Within this temperature range, the first PTFE microporous membrane 1 and the second PTFE microporous membrane 3... The porosity and pore size of the third PTFE microporous membrane 4 remain basically unchanged. Meanwhile, the micropores of the first PVDF microporous adhesive layer 2 and the PVDF microporous adhesive layer 4 are controlled to be open sponge-like micropores through a phase transformation process, and the pore size is larger than that of the first PTFE microporous membrane 1, the second PTFE microporous membrane 3 and the third PTFE microporous membrane 5. This ensures that the pore size of the composite ultra-thick perfluorinated microporous membrane remains basically unchanged. Given the acid resistance, oxidation resistance and high temperature resistance of PTFE and PVDF, the membrane meets the usage environment requirements of the super tantalum capacitor separator.

[0039] To meet the requirements of using ultra-thick perfluorinated microporous membranes as separators in super tantalum capacitors, the porosities of the first PTFE microporous membrane 1, the second PTFE microporous membrane 3, and the third PTFE microporous membrane 4 are 50%-90%, and the pore sizes are 0.03μm-1.0μm, preferably 0.05μm, 0.10μm, or 0.20μm. The first PVDF microporous adhesive layer and the second PVDF microporous adhesive layer are embedded in the surface pores of adjacent PTFE microporous membranes. The pore size of the PVDF microporous adhesive layer is larger than that of the PTFE microporous membrane to ensure the permeability of the ultra-thick perfluorinated microporous membrane. Properties; by controlling the micropores of the first PVDF microporous adhesive layer 2 and PVDF microporous adhesive layer 4 to be open sponge-like micropores through phase inversion process, the porosity of the ultra-thick perfluorinated microporous membrane is 50%-85%, the pore size is 0.03μm-1.0μm, and the thickness is 85μm-210μm. After phase inversion of PVDF and heat treatment between 170℃ and 185℃, the porosity of the ultra-thick perfluorinated microporous membrane is slightly lower than that of the single-layer PTFE microporous membrane, but the pore size of 0.03μm-1.0μm remains unchanged, which also keeps the flux of the ultra-thick perfluorinated microporous membrane basically unchanged. See Table 1 for details.

[0040] Table 1 Performance parameters of ultra-thick perfluorinated microporous membranes

[0041]

[0042] As can be seen from Table 1, the pore size of the ultra-thick perfluorinated microporous membranes in Examples 1 to 4 remains unchanged, but the porosity decreases and the water flux change rate is small. Both PTFE and PVDF can meet the requirements of acid resistance, oxidation resistance and high temperature environment of 100℃-150℃, which can meet the requirements of the separator of super tantalum capacitors. On the other hand, Comparative Examples 1 and 2 have large pore size changes and significantly reduced porosity, and the water flux change rate is also large, which cannot meet the requirements of the separator of super tantalum capacitors.

[0043] Example 2:

[0044] See Figure 2 This embodiment provides a process for preparing an ultra-thick perfluorinated microporous membrane, including the following steps:

[0045] Step S1: Prepare a first PTFE microporous membrane, a second PTFE microporous membrane, and a third PTFE microporous membrane with a thickness of 30μm-70μm by a stretching process. The porosity of the first PTFE microporous membrane 1, the second PTFE microporous membrane 3, and the third PTFE microporous membrane 4 are 50%-90%, and the pore size is 0.03μm-1.0μm, preferably 0.05μm, 0.10μm, or 0.20μm.

[0046] Step S2: Prepare PVDF adhesive solution; specifically, the preparation process of PVDF adhesive solution is as follows: select a single solvent or a mixed solvent, add the polymer material PVDF to the solvent and stir thoroughly to form PVDF adhesive solution, the content of PVDF is 0.5%-5%; the surface tension of the solvent is ≤ the surface tension of PVDF, the surface tension of PVDF is 25 dyn / cm; for example, the solvent can be acetone with a surface tension of 18.8 dyn / cm or butanone with a surface tension of 21.0 dyn / cm; the solvent can also be N,N-dimethyl... The adhesive uses one or a mixture of acetamide, N-methylpyrrolidone, and dimethyl sulfoxide, and one or a mixture of acetone and butanone, with surface tensions of 24 dyn / cm, 22 dyn / cm, 20 dyn / cm, etc. When the surface tension of the adhesive solvent is less than that of PVDF, the adhesive exhibits negative adsorption properties, resulting in a lower surface concentration of PVDF in the adhesive than the bulk concentration of the adhesive. During subsequent phase transformation, the micropores of the first PVDF microporous adhesive layer 2 and the second PVDF microporous adhesive layer 3 are open, sponge-like micropores.

[0047] Step S3: Immerse the second PTFE microporous membrane in the PVDF adhesive solution of step S2 to obtain an impregnated membrane; specifically, the amount of PVDF adhesive solution is quantitatively measured using a scraper, and the PVDF adhesive solution mainly adheres to the two surfaces of the second PTFE microporous membrane by adsorption force.

[0048] Step S4: The first PTFE microporous membrane, the impregnated membrane, and the third PTFE microporous membrane are successively processed through a composite process, a phase transformation process, and a heat treatment process to form the ultra-thick perfluorinated microporous membrane described in the first invention.

[0049] Specifically, the first PTFE microporous membrane, the impregnated membrane, and the third PTFE microporous membrane are composited using PVDF adhesive on both surfaces of the impregnated membrane as a binder. The composite membrane is then passed through an evaporation chamber at a speed of 0.5 m / min-3 m / min for phase transformation. The temperature of the evaporation chamber is 40℃-55℃, the humidity is 5%-25%, and the air velocity is 0.3 m / s-3 m / s, so that the solvent in the PVDF adhesive evaporates, forming a porous PVDF adhesive layer. Finally, the membrane is passed through a heat treatment chamber at a temperature of 170℃ to 185℃ at a speed of 0.3 m / min-3 m / min, so that the PVDF melts and acts as an adhesive to bond the first PTFE microporous membrane 1, the second PTFE microporous membrane 3, and the third PTFE microporous membrane 4 to form the ultra-thick perfluorinated microporous membrane described in Example 1. The performance parameters of the ultra-thick perfluorinated microporous membrane are shown in Table 1.

[0050] In the adhesive liquid of Example 2, the surface tension of the solvent is less than or equal to the surface tension of PVDF, forming a negatively adsorbed adhesive liquid. This results in the surface concentration of PVDF in the adhesive liquid being lower than the bulk concentration of the adhesive liquid. During the subsequent phase transformation, the surface pore size of the PVDF microporous adhesive layer will be larger than the pore size of the PTFE microporous membrane. This causes the micropores of the first PVDF microporous adhesive layer 2 and the second PVDF microporous adhesive layer 4 to exhibit an open, sponge-like characteristic, preventing the PVDF micropores from creating a blocking effect and ensuring the permeability of the ultra-thick perfluorinated microporous membrane.

[0051] The ultra-thick perfluorinated microporous membrane preparation process disclosed in this embodiment has the same technical solution as that in Embodiment 1. Please refer to Embodiment 1 for details, which will not be repeated here.

[0052] Example 3:

[0053] This embodiment provides an application whereby the ultra-thick perfluorinated microporous membrane described in Embodiment 1 is used as the separator for a super tantalum capacitor. Specifically, the separator of a super tantalum capacitor is exposed to a strong acid and high temperature environment, such as an electrolyte with a sulfuric acid concentration of 20%-50% and a temperature of 100℃-150℃. High thickness is also required for the separator. The ultra-thick perfluorinated microporous membrane of Embodiment 1 is composed of only PTFE and PVDF, both of which meet the requirements of acid resistance, oxidation resistance, and high temperature resistance. In particular, PTFE can operate stably at 200℃. When used as the separator for a super tantalum capacitor, the ultra-thick perfluorinated microporous membrane of this embodiment can withstand an ambient temperature of 100℃-150℃, ensuring the safety of the super tantalum capacitor.

[0054] The application of the ultra-thick perfluorinated microporous membrane disclosed in this embodiment has the same technical solution as that in Embodiment 1 and Embodiment 2. Please refer to Embodiment 1 and Embodiment 2 for details, which will not be repeated here.

Claims

1. An ultra-thick, perfluorinated microporous membrane characterized in that, The first PTFE microporous membrane, the first PVDF microporous adhesive layer, the second PTFE microporous membrane, the second PVDF microporous adhesive layer and the third PTFE microporous membrane are sequentially arranged from bottom to top. The thickness of the first PTFE microporous membrane, the second PTFE microporous membrane and the third PTFE microporous membrane is 30 μm-70 μm. The first PVDF microporous adhesive layer is located between the first PTFE microporous membrane and the second PTFE microporous membrane and is embedded into the surface membrane pores of the first PTFE microporous membrane and the second PTFE microporous membrane. The second PVDF microporous adhesive layer is located between the second PTFE microporous membrane and the third PTFE microporous membrane and is embedded into the surface membrane pores of the second PTFE microporous membrane and the third PTFE microporous membrane. The pore diameter of the first PVDF microporous adhesive layer and the second PVDF microporous adhesive layer is larger than the pore diameter of the first PTFE microporous membrane, the second PTFE microporous membrane and the third PTFE microporous membrane. The micropores of the first PVDF microporous adhesive layer and the second PVDF microporous adhesive layer are open sponge-like micropores and the pore diameter is larger than the pore diameter of the three layers of PTFE microporous membranes. The first PTFE microporous membrane, the first PVDF microporous adhesive layer, the second PTFE microporous membrane, the second PVDF microporous adhesive layer and the third PTFE microporous membrane are heat treated and bonded together, and when heat treatment is performed, the temperature needs to reach between 170℃ and 185℃, and the first PTFE microporous membrane, the second PTFE microporous membrane and the third PTFE microporous membrane can be bonded by the adhesive effect of PVDF.

2. The ultra-thick, perfluorinated microporous membrane of claim 1, wherein, The porosity of the first PTFE microporous membrane, the second PTFE microporous membrane and the third PTFE microporous membrane is 50%-90% and the pore diameter is 0.03 μm-1. 0 μm.

3. The ultra-thick, perfluorinated microporous membrane according to claim 1 or 2, characterized in that, The porosity of the super-thick perfluorinated microporous membrane is 50%-85%, the pore diameter is 0.03 μm-1. 0 μm, and the thickness is 85 μm-210 μm.

4. The super-thick perfluorinated microporous membrane according to any one of claims 1-3 is used as a separator in a super-tantalum capacitor.

5. Process for the preparation of ultra-thick perfluorinated microporous membranes, characterized in that, The method comprises the following steps: Step S1: preparing the first PTFE microporous membrane, the second PTFE microporous membrane and the third PTFE microporous membrane with a thickness of 30 μm-70 μm by a stretching process; Step S2: preparing a PVDF adhesive liquid; Step S3: immersing the second PTFE microporous membrane in the PVDF adhesive liquid of step S2 to obtain an immersed membrane; Step S4: the first PTFE microporous membrane, the immersed membrane and the third PTFE microporous membrane are sequentially subjected to a compounding process, a phase inversion process and a heat treatment process to form the super-thick perfluorinated microporous membrane according to any one of claims 1-3.

6. The process for making an ultrathick, perfluorinated microporous membrane according to claim 5, wherein, The method comprises the following steps: The porosity of the first PTFE microporous membrane, the second PTFE microporous membrane and the third PTFE microporous membrane is 50%-90% and the pore diameter is 0.03 μm-1. 0 μm.

7. The process for making an ultra-thick, perfluorinated microporous membrane according to claim 6, wherein, In step S3, the amount of PVDF adhesive liquid is quantitatively determined by a doctor blade.

8. The process for making an ultra-thick, perfluorinated microporous membrane according to claim 5 or 6, wherein, The preparation process of the PVDF adhesive liquid is as follows: A single solvent or mixed solvents are selected, and a polymer material PVDF is added into the solvent and stirred thoroughly to form a PVDF adhesive liquid, and the content of the PVDF is 0.5%-5%; The surface tension of the solvent is ≤ the surface tension of the PVDF.

Images