High-voltage-resistance and high-liquid-absorption composite electrolytic capacitor diaphragm and preparation method thereof

Abstract

The invention belongs to the field of paper for aluminum electrolytic capacitors, and particularly relates to a high-voltage-resistance and high-liquid-absorption composite electrolytic capacitor diaphragm and a preparation method thereof. The diaphragm is formed by compounding at least two layers of high-density base paper, and intermittent point-like bonding is carried out between the base paper through a hydrophilic high-molecular polymer according to the surface coating area of 10-40% and the gluing amount of 0.1-10g / m, so that the pore structure between the paper is reserved while the breakdown voltage is ensured to be increased, the liquid absorption capability is remarkably improved, and the equivalent series resistance (ESR) is reduced. The high-pressure diaphragm solves the problem that pressure resistance and liquid absorption performance of an existing high-pressure diaphragm are difficult to consider, and has the advantages of being simple in structure, excellent in electrical performance, suitable for large-scale production and the like.

Description

Technical Field

[0001] The invention belongs to the field of paper for aluminum electrolytic capacitors, and particularly relates to a high-voltage-resistant and high-liquid-absorbent composite electrolytic capacitor diaphragm and a preparation method thereof. Background Art

[0002] Electrolytic capacitors are important components in the electronics industry. Besides filtering, decoupling, and signal coupling, they also play a special role in specialized circuits such as rectification circuits, power supply circuits, and AC motor starting circuits. They are widely used in the automotive, security, medical electronics, computer and television, electronic toys, and industrial control industries.

[0003] Aluminum electrolytic capacitors typically consist of an anode aluminum foil, a cathode aluminum foil, an electrolyte, and an electrolytic capacitor diaphragm (commonly known as "electrolytic paper") located between the two electrodes. The diaphragm must provide sufficient dielectric strength at high DC voltages and, after impregnation, provide ample storage and transmission channels for the electrolyte, thereby achieving low equivalent series resistance (ESR) and excellent high-frequency performance. The industry generally uses high-density single-layer diaphragms made from plant fibers with high beating degrees to meet voltage requirements. However, the highly compacted fibers result in limited pores and low liquid absorption, often leading to high ESR. This makes it difficult to meet the dual requirements of high voltage resistance and low ESR required by high-power, small-sized electronic devices.

[0004] To balance voltage resistance and liquid absorption, one approach involves introducing a hydrophilic polymer adhesive layer between two or more layers of base paper. Chinese invention patent CN103021664A discloses that coating the entire surface of two layers of electrolytic paper with a starch / polyvinyl alcohol mixture and then laminating them together can increase the breakdown voltage by approximately 80V. However, the continuous coating of the adhesive on the paper significantly blocks pores, reducing the liquid content and permeation rate of the separator. This results in a relatively high ESR, making it difficult to meet high-current requirements.

[0005] Another common approach is to combine a high-density pressure-resistant layer with a low-density absorbent layer. For example, Chinese invention patent CN101187185A wet-presses a wood pulp layer with a 98° SR (beating degree) and a hemp / grass fiber layer with a 12–50° SR (beating degree) to achieve both functions within the same overall thickness. However, due to the high proportion of the low-density layer, the overall dielectric density is limited, resulting in a breakdown voltage lower than that of pure high-density paper at the same thickness. Furthermore, wet-pressing multiple layers can easily lead to overlapping puncture points, affecting reliability.

[0006] An earlier Chinese invention patent, CN100412270C, also used a multi-circular wire process to composite a wood pulp pressure-resistant layer with a multi-layer sisal / Manila hemp absorbent layer. While this improved the liquid absorption height, it made it difficult to exceed 900V per unit thickness and failed to effectively reduce ESR.

[0007] Chinese utility model CN204753253U reports the application of 5–25gm coating on the front side of cotton pulp-wood pulp composite base paper. -2 , Apply 0–10gm on the back -2 Coating to increase the withstand voltage 100Vmm -1 However, the thick coating further reduces the through pores, which is not conducive to the instantaneous absorption of the electrolyte and the ESR improvement is limited; at the same time, the coating tends to form a continuous and dense film layer, which is not conducive to the subsequent winding reliability.

[0008] The above existing technologies show that while continuous large-area polymer coating can improve voltage resistance, it fills the fiber pores and inhibits capillary action. While introducing a low-density absorption layer can improve liquid content, it sacrifices voltage resistance per unit thickness, making it difficult to balance device size, voltage resistance, and ESR. The industry urgently needs a new composite diaphragm structure and preparation method that can: 1. maintain high density and high breakdown voltage while 2. not significantly reducing effective porosity and capillary network; 3. rapidly absorb electrolyte and significantly reduce ESR; 4. meet the development trend of aluminum electrolytic capacitors with rated voltages above 100V, large ripple currents, and miniaturization. Summary of the Invention

[0009] In order to overcome the shortcomings of the existing technology that it is difficult to simultaneously meet the requirements of high breakdown voltage and low ESR, the present invention provides a composite electrolytic capacitor diaphragm, which can significantly improve the voltage resistance of the diaphragm, while having excellent liquid absorption performance and significantly reducing the ESR value of the electrolytic capacitor.

[0010] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: A high-voltage, high-liquid-absorbency composite electrolytic capacitor diaphragm, comprising at least two layers of high-density electrolytic capacitor base paper stacked sequentially in the thickness direction and composited by hot pressing and drying. Each layer of base paper is obtained by wet forming, pressing, and drying plant fibers having a beating degree of 92°SR-98°SR. Adjacent base papers are provided with an adhesive layer and meet the following requirements: 1) The adhesive layer is composed of a hydrophilic polymer; 2) The adhesive layer is dispersed in a discontinuous intermittent pattern only on a single side of at least one layer of base paper, and the polymer coating area occupies 10-40% of the effective area of ​​the side surface; 3) The polymer coating amount is 0.1-10g / m².

[0011] Preferably, the polymer coating area accounts for 10%, 15%, 20%, 25%, 30%, 35% or 40% of the effective area of ​​the side surface.

[0012] Preferably, the polymer glue amount is 0.2g / m², 0.3g / m², 0.4g / m², 0.5g / m², 0.6g / m², 0.7g / m², 0.8g / m², 0.9g / m², 1.0g / m², 2.0g / m², 3.0g / m², 4.0g / m², 5.0g / m², 6.0g / m², 7.0g / m², 8.0g / m², 9.0g / m² or 10g / m². If the amount of glue applied is too little, the base paper will have poor adhesion and will easily delaminate during the slitting and winding process, resulting in product scrap. If the amount of glue applied is too high, the paper will be too tightly bonded, which will reduce the porosity between the base papers and hinder the absorption of electrolyte.

[0013] Preferably, the polymer is a hydrophilic natural polymer or a hydrophilic synthetic polymer, the hydrophilic natural polymer is one or more of starch, chitosan, carboxymethyl cellulose, and hydroxypropyl cellulose, and the hydrophilic synthetic polymer is one or more of polyvinyl alcohol, polyacrylic acid, and polyacrylamide.

[0014] Preferably, the plant fiber is wood pulp, hemp pulp or a combination thereof.

[0015] As a preference, the density of each base paper is 0.88-0.92 g / cm 3 , optional: 0.88, 0.89, 0.90, 0.91, 0.92g / cm 3 .

[0016] Preferably, the bonding layer pattern is a dot-shaped or strip-shaped distribution formed by circular, strip-shaped or polygonal grooves.

[0017] Preferably, the polymer is starch or polyvinyl alcohol, and its number average molecular weight is 1×10 4 -2×10 5 .

[0018] Preferably, 0.1-5wt% of a cross-linking agent is further added to the polymer. The cross-linking agent is selected from one or more of glutaraldehyde, citric acid, tartaric acid, boric acid, 1,2-propylene oxide, sodium tripolyphosphate and N,N'-methylenebisacrylamide. The polymer adhesive material used in this patent is a hydrophilic natural polymer or a hydrophilic synthetic polymer. In order to further improve its heat resistance, electrolyte resistance and bonding stability, an appropriate amount of cross-linking agent can be added to the polymer coating liquid to achieve partial cross-linking and curing of the molecular structure. The cross-linking agent is related to the polymer system, and the recommended combination is as follows:

[0019] Preferably, the separator has a thickness of 25-60 μm, and according to GB / T461.1-2002 Paper and paperboard - Determination of capillary absorption height (Krem method), the water absorption height in 10 minutes is ≥50 mm.

[0020] Furthermore, the present invention also provides a method for preparing the composite diaphragm, which comprises the following steps: 1) Using plant fiber with a beating degree of 92°SR-98°SR and a pulp concentration of 0.3-0.7%, forming through a Fourdrinier wire, pressing and drying to obtain high-density base paper; 2) coating one side of the base paper with a hydrophilic polymer solution intermittently by gravure coating or spray coating, with the coating area accounting for 10-40%, the polymer solution concentration being 1-10%, and the temperature being 40-80°C; 3) Two or more sheets of base paper treated in step 2) are laminated with the coated surfaces facing each other, and then laminated by pressing and drying in a multi-stage drying cylinder at 30-90°C, with the glue amount controlled at 0.1-10g / m² to obtain the target separator.

[0021] Preferably, step 2) uses a gravure coating roller with circular grooves on the surface, and the groove area accounts for 25-35% of the roller surface.

[0022] Preferably, in step 3), the number of drying cylinders is 3-10, and the drying temperature is gradually increased and then decreased in the direction of paper web running; and before lamination, a linear pressure of 0.1-1 MPa is applied to enhance bonding between base papers.

[0023] The present invention utilizes the aforementioned technical solution, forming a composite of two or more layers of high-density electrolytic capacitor base paper. The base papers are bonded together using a hydrophilic polymer. The polymer is not entirely coated on the base paper surface, but rather occupies only a portion of the base paper surface. This creates a rich porous structure between the base papers after the composite, resulting in a strong capillary effect. Compared to the prior art, the present invention has the following beneficial effects: 1. Significantly Improved Voltage Withstand Per Unit Thickness: By coating a hydrophilic polymer only in localized intermittent areas and dot-gluing two (or more) layers of high-density base paper, this invention creates a dual-reinforcement system: a dense fiber skeleton and dispersed glue bridges. This structure improves the uniformity of electric field distribution and inter-fiber bonding strength without increasing overall thickness, resulting in a composite separator with a breakdown voltage 1.2–1.5 times that of a single layer of base paper.

[0024] 2. Significantly Reduced Equivalent Series Resistance (ESR): The polymer's hydrophilicity and discontinuous dot distribution preserve the interpenetrating pores between the base paper, forming a highly efficient capillary network. This network absorbs and securely retains large amounts of electrolyte immediately after impregnation. This simultaneously reduces electrolyte impedance and ion diffusion resistance, ultimately resulting in a 20–30% reduction in ESR.

[0025] 3. The liquid absorption speed and liquid retention capacity are greatly improved: After compounding, the average pore size and connectivity between the base papers are enhanced, and the 10-minute water absorption height is increased from 2-4mm of the traditional high-density single-layer diaphragm to ≥60mm, ensuring the liquid phase compensation capability under large ripple current conditions and suppressing temperature rise and electrolyte drying.

[0026] 4. Size-Performance Co-Optimization: Traditional high-low density layering schemes sacrifice voltage resistance and increase overall thickness to achieve liquid absorption. This invention achieves both high voltage resistance and high liquid absorption without requiring a low density layer, allowing for further device miniaturization while increasing the rated voltage, meeting the latest demand for 105°C, ≥100V aluminum electrolytic capacitors in high-power density power supplies and automotive electronics.

[0027] 5. Simple process, high reliability: The process utilizes gravure or spray-coating for one-time dot-coating, followed by conventional drying. Lamination is completed without the need for multi-web wet pressing or thick film coating, resulting in low production line modification costs and high yield rates. The dot-coating prevents misalignment of the base paper during the winding process and avoids excessive adhesion that could lead to loss of interlayer porosity. The composite separator exhibits no delamination or premature failure due to breakdown during slitting, winding, or prolonged heat loads.

[0028] In summary, the present invention achieves a synergistic breakthrough in the three key performances of high breakdown voltage, low ESR, and high liquid absorption rate through the simple structural design of high-density base paper and intermittent hydrophilic dispensing. It is significantly superior to the existing technologies of overall coating and high-low density layered types, and has outstanding industrialization and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the cross section of the composite diaphragm, where 1 is the upper base paper, 2 is the adhesive layer, and 3 is the lower base paper.

[0030] Figure 2 Schematic diagram of the gluing points on the surface of the diaphragm after compounding, where 4 is the unglued area on the surface of the base paper, and 5 is the gluing area on the surface of the base paper. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0032] Example 1 Preparation of base paper: The wood pulp was beaten by a disc grinder with a beating degree of 95°SR. After beating, the wood pulp was formed by a fourdrinier wire with a forming concentration of 0.5%. After forming, the wood pulp was pressed, dried, and rolled to obtain base paper A with a thickness of 15.0 μm.

[0033] Preparation of double-layer composite paper: The base paper A is divided into two rolls, and the first and second rolls are coated with a gravure coating roller. The gravure coating roller pattern is a circular groove, and the area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating roller. The coating liquid is an aqueous solution of starch. The coating liquid temperature is 40°C, the coating liquid concentration is 5.0%, and the glue amount of the composite paper after coating is 0.5g / m2. After coating, the first and second rolls coated with the starch solution are composited, and then pressed. Then, 8 drying cylinders are used for drying. The drying temperatures are 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 70°C, and 60°C, respectively. After drying, the rolls are rolled up and then slit to obtain a final product with a thickness of 30.5μm (such as Figure 1 、 Figure 2 shown).

[0034] Example 2 Preparation of base paper: The wood pulp was beaten by a disc grinder with a beating degree of 95°SR. After beating, the wood pulp was formed by a fourdrinier wire with a forming concentration of 0.5%. After forming, the wood pulp was pressed, dried, and rolled to obtain base paper A with a thickness of 20.0 μm.

[0035] Preparation of double-layer composite paper: The base paper A is divided into two rolls. The first and second rolls are coated with a gravure coating roller. The pattern of the gravure coating roller is a circular groove. The area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating roller. The coating liquid is an aqueous solution of starch. The coating liquid temperature is 40°C, the coating liquid concentration is 6.0%, and the amount of glue on the composite paper after coating is 0.8 g / m2. After coating, the first and second rolls coated with the starch solution are compounded, and then pressed. Then, 8 drying cylinders are used for drying. The drying temperatures are 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 70°C, and 60°C, respectively. After drying, the rolls are rolled up and then slit to obtain a final product with a thickness of 40.8 μm.

[0036] Example 3 Preparation of base paper: The hemp pulp was beaten with a disc grinder at a beating degree of 95°SR. After beating, the hemp pulp was formed using a fourdrinier wire at a forming concentration of 0.5%. After forming, the pulp was pressed, dried, and rolled to obtain base paper A with a thickness of 15.0 μm.

[0037] Preparation of double-layer composite paper: The base paper A is divided into two rolls. The first and second rolls are coated with a gravure coating roller. The pattern of the gravure coating roller is a circular groove. The area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating roller. The coating liquid is an aqueous solution of starch. The coating liquid temperature is 40°C, the coating liquid concentration is 5.0%, and the amount of glue on the composite paper after coating is 0.5g / m2. After coating, the first and second rolls coated with the starch solution are compounded, and then pressed. Then, 8 drying cylinders are used for drying. The drying temperatures are 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 70°C, and 60°C, respectively. After drying, the rolls are rolled up and then slit to obtain a final product with a thickness of 30.5μm.

[0038] Example 4 Preparation of base paper: The hemp pulp was beaten with a disc grinder at a beating degree of 95°SR. After beating, the hemp pulp was formed with a fourdrinier wire at a forming concentration of 0.5%. After forming, the pulp was pressed, dried, and rolled to obtain base paper A with a thickness of 20.0 μm.

[0039] Preparation of double-layer composite paper: The base paper A is divided into two rolls. The first and second rolls are coated with a gravure coating roller. The pattern of the gravure coating roller is a circular groove. The area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating roller. The coating liquid is an aqueous solution of starch. The coating liquid temperature is 40°C, the coating liquid concentration is 6.0%, and the amount of glue on the composite paper after coating is 0.8 g / m2. After coating, the first and second rolls coated with the starch solution are compounded, and then pressed. Then, 8 drying cylinders are used for drying. The drying temperatures are 40°C, 45°C, 50°C, 60°C, 70°C, 80°C, 70°C, and 60°C, respectively. After drying, the rolls are rolled up and then slit to obtain a final product with a thickness of 40.8 μm.

[0040] Example 5 The same as in Example 1, the coating liquid is a 5 wt % PVA aqueous solution (polymerization degree 1700±100, alcoholysis degree 98%, heat preservation at 40° C.), and the other technical features are the same as in Example 1.

[0041] Example 6 As in Example 1, the coating liquid is a 4 wt % sodium polyacrylate solution (molecular weight ≈ 500,000, pH adjusted to 6.5), and other technical features are the same as in Example 1.

[0042] Example 7 As in Example 1, the dispensing coating liquid is as follows: Main agent: 5wt% starch aqueous solution; Additives: 0.5wt% glutaraldehyde (based on dry starch); Coating liquid temperature: 40℃, stir evenly and react for 30 minutes; Other technical features are the same as those in Example 1.

[0043] Comparative Example 1 The wood pulp is beaten by a disc grinder with a beating degree of 95.0°SR. After beating, the wood pulp is formed by a fourdrinier mesh with a forming concentration of 0.5%. After forming, it is pressed, dried, and wound, and then slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 15.0μm.

[0044] Comparative Example 2 The wood pulp is beaten by a disc grinder with a beating degree of 94.5°SR. After beating, the wood pulp is formed by a fourdrinier with a forming concentration of 0.5%. After forming, it is pressed, dried, and wound, and then slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 30.2μm.

[0045] Comparative Example 3 The wood pulp is beaten by a disc grinder with a beating degree of 94.5°SR. After beating, the wood pulp is formed by a fourdrinier with a forming concentration of 0.5%. After forming, it is pressed, dried, and wound, and then slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 40.1μm.

[0046] Comparative Example 4 The hemp pulp is beaten by a disc grinder with a beating degree of 95.0°SR. After beating, the hemp pulp is formed by a long wire mesh. After forming, it is pressed, dried, and rolled. After slitting, a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 15.0 μm is obtained.

[0047] Comparative Example 5 The hemp pulp is beaten by a disc grinder with a beating degree of 94.5°SR. After beating, the hemp pulp is formed by a long wire mesh. After forming, it is pressed, dried, and rolled. After slitting, a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 30.2 μm is obtained.

[0048] Comparative Example 6 The hemp pulp is beaten by a disc grinder with a beating degree of 94.5°SR. After beating, the hemp pulp is formed by a long wire mesh. After forming, it is pressed, dried, and rolled. After slitting, a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 40.3 μm is obtained.

[0049] Comparative Example 7 Wood pulp was refined with a disc refiner to a beating degree of 94.5°SR. After beating, the wood pulp was formed using a Fourdrinier wire mesh at a forming consistency of 0.5%. Cotton pulp was refined with a disc refiner to a beating degree of 35°SR. After beating, the cotton pulp was formed using a rotary wire mesh at a forming consistency of 0.02%. After forming, the Fourdrinier wire layer and the rotary wire layer were composited, then pressed, dried, and wound. After slitting, a high-voltage double-layer electrolytic capacitor diaphragm with a thickness of 40.5μm was obtained.

[0050] Comparative Example 8 Hemp pulp was refined with a disc mill to a beating degree of 94.5°SR. After beating, the hemp pulp was formed using a Fourdrinier wire mesh at a forming consistency of 0.5%. Cotton pulp was refined with a disc mill to a beating degree of 35°SR. After beating, the cotton pulp was formed using a rotary mesh mesh at a forming consistency of 0.02%. After forming, the Fourdrinier wire layer and the rotary mesh layer were composited, then pressed, dried, and wound. After slitting, a high-voltage double-layer electrolytic capacitor diaphragm with a thickness of 40.5μm was obtained.

[0051] Comparative Example 9 As in Example 1, two sheets of 15 µm wood pulp paper were bonded together with a continuous, full-surface 10 g / m² PVA coating having a thickness of 30.6 µm. Other technical features were the same as in Example 1.

[0052] Comparative Example 10 As in Example 1, two sheets of 15 µm wood pulp paper were laminated with a hydrophobic polyethylene wax adhesive at a concentration of 0.6 g / m² (30% area), resulting in a thickness of 30.5 µm. Other technical features were the same as in Example 1.

[0053] Comparative Example 11 As in Example 1, two sheets of 15 µm wood pulp base paper were used for papermaking, with a beating degree of 70° SR and a thickness of 30.4 µm. Other technical features were the same as in Example 1.

[0054] Test Example 1 The process parameters and test results for four examples and 11 comparative examples are given below (as shown in Table 1). Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in the present invention can be purchased commercially or prepared by existing methods. The testing methods used in the comparative examples and examples are as follows: Tightness: GB / T451.3; Thickness: GB / T451.3; Breakdown voltage: GB / T12913; Water absorption height: GB / T461.1; ESR: The diaphragm was prepared into a capacitor and measured using an LCR meter at a temperature of 20°C and a frequency of 1 kHz.

[0055] Table 1 is the process parameters and test results

[0056] Data Analysis: 1. Breakdown voltage Advantage in withstand voltage per unit thickness: Measured in "V / µm", Examples 1-4 respectively improve by 30-55% compared with the corresponding controls, reaching a maximum of 43-44V / µm (Example 1, Comparative Example 10), proving that the local hydrophilic dispensing + composite structure significantly enhances the electric field uniformity and fiber skeleton strength.

[0057] Comparison of continuous full-surface coating (Comparative Example 9): The thickness is close to that of Example 1, but the voltage is only 1150V, indicating that large-area film will produce defective interfaces and weaken the electric field distribution.

[0058] Comparison of hydrophobic dispensing (Comparative Example 10): Although the breakdown voltage can reach 1350V, it is still lower than that of Example 1; the subsequent liquid absorption and ESR indicators are even worse, verifying that "hydrophilicity" is the key to improving comprehensive performance.

[0059] 2. Liquid absorption performance (10min water absorption height) The water absorption height of high-density single-layer comparative examples 1 to 6 is only 2-3 mm; the water absorption height of wet-layered comparative examples 7 and 8 is slightly higher, up to 4 mm.

[0060] The liquid absorption height of the embodiment is 58-87 mm, which is increased by 20-30 times; this is due to the large number of interconnected pores retained between the base paper and the fast capillary channels provided by the hydrophilic dispensing.

[0061] The thicknesses of Comparative Example 9 (whole-surface PVA) and Comparative Example 10 (hydrophobic wax dispensing) are only 6 mm and 8 mm, respectively, further confirming that the synergistic effect of intermittent + hydrophilic is irreplaceable.

[0062] 3. Equivalent series resistance (ESR, 1kHz, 20℃) The reduction in ESR is directly related to the amount of liquid absorbed: the hydrophilic dispensing compound significantly increases the liquid content and shortens the ion migration path, thereby reducing the impedance.

[0063] Even though the breakdown voltage of Comparative Examples 9 and 10 is relatively high, the ESR is still as high as 1.90Ω and 1.85Ω, which does not reach the level of the embodiment. This once again shows that thick coating or hydrophobic-based adhesive alone cannot achieve low ESR.

[0064] 4. Density and Structural Explanation The tightness of the embodiment and the single-layer high-density control is maintained at 0.90-0.92gcm -3 This shows that the present invention achieves higher pressure resistance and liquid absorption through "hydrophilic intermittent dispensing + double-layer high-density base paper" without reducing the density; the performance improvement is not at the expense of a loose structure.

[0065] The density of the delaminated wet web samples (Comparative Example 7 / Comparative Example 8) is significantly lower (≈0.80 gcm -3 ), although the liquid absorption is slightly better than that of a single layer, the pressure resistance is seriously reduced, which proves that the low-density strategy is difficult to achieve a simultaneous improvement of the two indicators.

[0066] 5. Conclusion Optimal overall performance: The embodiment simultaneously achieves high breakdown voltage, ultra-high liquid absorption rate, and low ESR at the same or thinner thickness, meeting the stringent requirements of high power density aluminum electrolytic capacitors for high withstand voltage and low impedance.

[0067] Test Example 2 Objective: System verification: A) polymer coating area accounts for 10%–40% of the paper surface area, B) polymer coating weight is 0.1gm -2 –10gm -2 ; The combined impact of these two process windows on the diaphragm breakdown voltage, liquid absorption and ESR.

[0068] 1. Experimental plan

[0069] Using L9(3 2 ) orthogonal table; the remaining conditions are exactly the same as those in Example 1 (15µm×2 starch dispensing, gravure 8-stage gradient drying).

[0070] Three rolls were prepared for each group of samples and the average value was taken for testing. The testing method was the same as that in the instructions - GB / T451.3, GB / T12913, GB / T461.1 and 1kHzESR determination.

[0071] 2. Test results (average value)

[0072] 3. Range and trend analysis

[0073] Breakdown voltage: increases with the coating area and the amount of glue applied, but the growth curve tends to saturation; the effect of factor A is slightly stronger than that of factor B.

[0074] Liquid absorption height: It decreases significantly with the area or amount of glue. The extreme difference indicates that the amount of glue is too high (10gm -2 ) has the most serious inhibition on liquid absorption.

[0075] ESR: The lowest value occurs when A=25%, B=1gm -2 ; Excessive glue amount causes ESR to rise.

[0076] 4. Comprehensive evaluation (weighted method) Let breakdown voltage↑(+), water absorption↑(+), ESR↓(–); assign weights 0.4:0.3:0.3 to calculate the comprehensive score. The highest result is still group 5 (25% / 1gm -2 ).

[0077] 5. Technical Effect 1) When the coating area is less than 10%, the adhesion is insufficient and the breakdown voltage drops to below 1100V. When the coating area is 40%, the water absorption drops sharply to <15mm and the ESR is greater than 1.9Ω. Therefore, the coating area of ​​10–40% is the optimal range to ensure high withstand voltage while avoiding excessive closure of the capillary network.

[0078] 2) Glue amount <0.1gm -2 Easy to delaminate when compounding; glue amount 10gm -2 When the pores are flooded, water absorption <10mm, ESR>2Ω; glue amount 0.1–10gm -2 It covers the feasible process range from "minimum bonding requirements" to "critical pore blocking".

[0079] 3) Optimal combination (25% / 1gm -2 The breakdown voltage reaches 1324V (+55% compared to the 30µm single-layer benchmark), the water absorption is 62mm (20 times that of the 3mm benchmark), and the ESR is 1.48Ω (down 10% from the single-layer benchmark of 1.65Ω), fully reflecting the coordinated improvement of the three indicators of high voltage resistance, high liquid absorption and low ESR.

[0080] The above is a description of the embodiments of the present invention. The above description of the disclosed embodiments will enable professionals in the field to implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-voltage and high-liquid-absorbent composite electrolytic capacitor diaphragm, characterized in that: The invention comprises at least two layers of high-density electrolytic capacitor base paper stacked in sequence along the thickness direction and laminated by hot pressing and drying. Each layer of base paper is obtained by wet forming, pressing and drying plant fibers with a beating degree of 92°SR-98°SR. Adjacent base papers are provided with a bonding layer and meet the following requirements: 1) The adhesive layer is composed of a hydrophilic polymer; 2) The adhesive layer is dispersed in a discontinuous intermittent pattern only on a single side of at least one layer of base paper, and the polymer coating area occupies 10-40% of the effective area of ​​the side surface; 3) The polymer coating amount is 0.1-10g / m².

2. The diaphragm according to claim 1, characterized in that The polymer is selected from a mixture of one or more of starch, chitosan, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyacrylic acid or polyacrylamide.

3. The diaphragm according to claim 1, characterized in that The plant fiber is wood pulp, hemp pulp or a combination thereof; the density of each base paper is 0.88-0.92g / cm³.

4. The diaphragm according to claim 1, characterized in that The bonding layer pattern is a dot-shaped or strip-shaped distribution formed by circular, strip-shaped or polygonal grooves.

5. The diaphragm according to claim 1, characterized in that The polymer is starch or polyvinyl alcohol, and its number average molecular weight is 1×10 4 -2×10 5 .

6. The diaphragm according to claim 1, characterized in that 0.1-5 wt% of a cross-linking agent is also added to the polymer.

7. The diaphragm according to claim 1, characterized in that The thickness of the diaphragm is 25-60 μm, and the water absorption height in 10 minutes is ≥50 mm.

8. A method for preparing the diaphragm according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: 1) Using plant fiber with a beating degree of 92°SR-98°SR and a pulp mass concentration of 0.3-0.7%, forming through a Fourdrinier wire, pressing and drying to obtain high-density base paper; 2) coating one side of the base paper with a hydrophilic polymer solution intermittently by gravure coating or spray coating, with the coating area accounting for 10-40%, the polymer solution mass concentration being 1-10%, and the temperature being 40-80°C; 3) Two or more sheets of base paper treated in step 2) are laminated with the coated surfaces facing each other, and then laminated by pressing and drying in a multi-stage drying cylinder at 30-90°C, with the glue amount controlled at 0.1-10g / m² to obtain the target separator.

9. The method according to claim 8, characterized in that Step 2) Use a gravure coating roller with circular grooves on the surface, where the groove area accounts for 25-35% of the roller surface.

10. The method according to claim 8 or 9, characterized in that Step 3) The number of drying cylinders is 3-10, and the drying temperature is gradually increased and then decreased in the direction of paper web running; before lamination, a linear pressure of 0.1-1 MPa is applied to enhance the bonding between the base papers.

Images