A high-voltage-resistant and high-liquid-absorption composite electrolytic capacitor separator and a preparation method thereof

Abstract

The application belongs to the field of aluminum electrolytic capacitor paper, and particularly relates to a high-voltage-resistant and high-liquid-absorbing composite electrolytic capacitor diaphragm and a preparation method thereof. The diaphragm is composed of at least two layers of high-density base paper, and the base papers are intermittently and punctiformly bonded by a hydrophilic polymer with a surface coating area of 10% to 40% and a gumming amount of 0.1 to 10 g / m2, so as to ensure the improvement of the breakdown voltage and the reservation of the pore structure between the papers, significantly improve the liquid absorption capacity and reduce the equivalent series resistance (ESR). The application solves the problem that the existing high-voltage diaphragm is difficult to have both pressure resistance and liquid absorption, and has the advantages of simple structure, excellent electrical performance, and suitability for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of paper for aluminum electrolytic capacitors, specifically relating to a high voltage-resistant and high liquid-absorbing composite electrolytic capacitor separator and its preparation method. Background Technology

[0002] Electrolytic capacitors are essential components in the electronics industry. Besides their functions of filtering, decoupling, and signal coupling in circuits, they also play special roles in specialized circuits such as correction 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 separator (commonly known as "electrolytic paper") located between the two electrodes. The separator must provide sufficient dielectric strength under high DC voltages and, after impregnation, provide ample storage and transport channels for the electrolyte, thereby achieving low equivalent series resistance (ESR) and excellent high-frequency performance. The industry commonly uses high-density single-layer separators made from highly pulped plant fibers to meet voltage withstand requirements. However, the high compaction of the fibers restricts capillary pores, resulting in low liquid absorption and often leading to persistently high ESRs, making it difficult to meet the dual requirements of high voltage withstand and low ESR in high-power, small-size electronic devices.

[0004] To balance pressure resistance and liquid absorption, one approach is to introduce 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 before laminating can increase the breakdown voltage by about 80V; however, the continuous coverage of the adhesive on the paper surface significantly blocks the pores, reduces the liquid content and permeation rate of the diaphragm, and the ESR remains high, making it difficult to meet the requirements of high-current scenarios.

[0005] Another common approach is to use a high-density pressure-resistant layer combined with a low-density absorbent layer. For example, Chinese invention patent CN101187185A wet-processes a wood pulp layer with a freeness of 98°SR and a hemp / grass fiber layer with a freeness of 12–50°SR, attempting to achieve both functions within the same total thickness. However, due to the high proportion of the low-density layer, the overall dielectric density is limited, and the breakdown voltage at the same thickness is still lower than that of pure high-density paper. Furthermore, multi-layer wet-pressed composites are prone to overlapping puncture points, affecting reliability.

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

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

[0008] The existing technologies described above demonstrate that while continuous large-area polymer coating can improve withstand voltage, it also clogs fiber pores and inhibits capillary action. Conversely, introducing a low-density absorber layer can improve electrolyte content, but sacrifices withstand voltage per unit thickness, making it difficult to simultaneously achieve optimal device size, withstand voltage, and ESR. The industry urgently needs a new composite diaphragm structure and preparation method to meet the following requirements: 1. Maintaining high density and high breakdown voltage; 2. Not significantly reducing effective porosity and capillary network; 3. Rapidly retaining electrolyte and significantly reducing ESR; 4. Meeting the development trend of aluminum electrolytic capacitors with rated voltages above 100V, large ripple currents, and miniaturization. Summary of the Invention

[0009] To overcome the drawback of existing technologies where it is difficult to simultaneously achieve both high breakdown voltage and low ESR, this invention provides a composite electrolytic capacitor separator that can significantly improve the separator's voltage withstand capability while also exhibiting excellent liquid absorption properties, thus significantly reducing the ESR value of the electrolytic capacitor.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A high-voltage-resistant, high-absorbency composite electrolytic capacitor separator comprises at least two layers of high-density electrolytic capacitor base paper stacked sequentially along the thickness direction and laminated by hot pressing and drying. Each base paper is obtained by wet forming, pressing, and drying of plant fibers with a freeness of 92°SR-98°SR. An adhesive layer is provided between adjacent base papers, and the following conditions are met:

[0012] 1) The adhesive layer is composed of a hydrophilic polymer;

[0013] 2) The adhesive layer is dispersed only on one side of at least one layer of base paper in a discontinuous, intermittent pattern, and the polymer coating area accounts for 10-40% of the effective area of ​​that side surface;

[0014] 3) The amount of polymer applied is 0.1-10 g / m².

[0015] Preferably, the polymer coating area accounts for 10%, 15%, 20%, 25%, 30%, 35%, or 40% of the effective area of ​​the side surface.

[0016] Preferably, the polymer coating amount is 0.2 g / m², 0.3 g / m², 0.4 g / m², 0.5 g / m², 0.6 g / m²,

[0017] 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,

[0018] 7.0g / m², 8.0g / m², 9.0g / m², or 10g / m². Too little adhesive will result in poor adhesion of the base paper, making it prone to delamination during slitting and winding, leading to product scrap. Too much adhesive will result in the paper being bonded too tightly, reducing the porosity between the base paper layers and hindering electrolyte absorption.

[0019] 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.

[0020] Preferably, the plant fiber is wood pulp, hemp pulp, or a combination thereof.

[0021] Preferably, the density of each base paper is 0.88-0.92 g / cm³. 3 The selectable values ​​are 0.88, 0.89, 0.90, 0.91, and 0.92 g / cm³. 3 .

[0022] Preferably, the adhesive layer pattern is a dotted or striped distribution formed by circular, striped, or polygonal grooves.

[0023] Preferably, the polymer is starch or polyvinyl alcohol, and its number average molecular weight is 1×10⁻⁶. 4 -2×10 5 .

[0024] Preferably, 0.1-5 wt% of a crosslinking agent is also added to the polymer. The crosslinking agent is selected from one or more of glutaraldehyde, citric acid, tartaric acid, boric acid, 1,2-epoxypropane, sodium tripolyphosphate, and N,N'-methylenebisacrylamide. The polymeric adhesive material used in this patent is a hydrophilic natural polymer or a hydrophilic synthetic polymer. To further improve its heat resistance, electrolyte resistance, and adhesion stability, an appropriate amount of crosslinking agent can be added to the polymer coating solution to achieve partial crosslinking and curing of the molecular structure. The crosslinking agent is related to the polymer system; recommended combinations are as follows:

[0025]

[0026] Preferably, the diaphragm thickness is 25-60 μm, and according to GB / T461.1-2002 Determination of capillary liquid absorption height of paper and paperboard (Klem method), the water absorption height is ≥50 mm in 10 min.

[0027] Furthermore, the present invention also provides a method for preparing the composite membrane, the method comprising the following steps:

[0028] 1) High-density base paper is obtained by pulping plant fibers with a freeness of 92°SR-98°SR and a pulp concentration of 0.3-0.7%, followed by wire forming, pressing and drying.

[0029] 2) The base paper is intermittently coated with a hydrophilic polymer solution on one side 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℃.

[0030] 3) Two or more sheets of base paper treated in step 2) are bonded together with the coated surfaces facing each other, and then dried and laminated by pressing and multi-stage heating cylinder at 30-90℃, controlling the amount of adhesive to be applied to be 0.1-10g / m², to obtain the target diaphragm.

[0031] Preferably, step 2) uses a gravure coating roller with a circular groove on the surface, the groove area accounting for 25-35% of the roller surface.

[0032] Preferably, the number of drying cylinders in step 3) is 3-10, and the drying temperature is gradually increased and then gradually decreased in the direction of paper web movement; before lamination, a linear pressure of 0.1-1 MPa is applied to enhance the bonding between the base papers.

[0033] This invention, employing the aforementioned technical solution, comprises a composite of double-layer or multi-layer high-density electrolytic capacitor paper. The paper layers are bonded together with a hydrophilic polymer. The polymer is not entirely coated on the surface of the paper, but only occupies a portion of its area, resulting in a highly porous structure between the composite layers, exhibiting a strong capillary effect. Compared to existing technologies, the advantages of this invention are:

[0034] 1. Significantly Improved Voltage Resistance per Unit Thickness: By coating hydrophilic polymers only in locally intermittent areas and dot-bonding two (or more) layers of high-density base paper, this invention forms a dual-reinforcement system of a dense fiber skeleton and dispersed dot-bonded bridges. This structure improves the uniformity of electric field distribution and the bonding strength between fibers without increasing the total thickness, enabling the breakdown voltage of the composite diaphragm to reach 1.2–1.5 times that of the corresponding single-layer base paper.

[0035] 2. Significantly reduced equivalent series resistance (ESR): The hydrophilicity of the polymer and its discontinuous point distribution together preserve the interconnected pores between the base paper, forming a highly efficient capillary network. This network can absorb and firmly retain a large amount of electrolyte at the moment of impregnation, and the electrolyte resistance and ion diffusion resistance decrease simultaneously, ultimately resulting in a 20-30% reduction in ESR.

[0036] 3. Significantly improved liquid absorption speed and liquid retention: The average pore size and connectivity between the base paper layers are enhanced after lamination. The water absorption height in 10 minutes is increased from 2–4 mm in traditional high-density single-layer membranes to ≥60 mm, ensuring the liquid phase compensation capability under high ripple current conditions and suppressing temperature rise and electrolyte drying.

[0037] 4. Size-Performance Co-optimization: Traditional high-low density layering schemes must sacrifice voltage withstand capability and increase overall thickness to achieve liquid absorption. This invention achieves both high voltage withstand capability and high liquid absorption without the need for a low density layer, allowing for further miniaturization of the device while maintaining or increasing the rated voltage. This meets the latest requirements of high power density power supplies and automotive electronics for 105℃, ≥100V aluminum electrolytic capacitors.

[0038] 5. Simple process and high reliability: The lamination process is completed by applying adhesive in a single dotted application using gravure or spraying, followed by conventional drying in a drying cylinder. This eliminates the need for multi-wire wet pressing or thick-film overall coating, resulting in low production line modification costs and a high yield rate. The dotted adhesive bonding prevents misalignment of the base paper during winding and avoids excessive adhesion that could lead to loss of interlayer porosity. The composite separator did not exhibit delamination or premature failure under slitting, winding, or long-term heat load.

[0039] In summary, this invention achieves a synergistic breakthrough in three key performance aspects—high breakdown voltage, low ESR, and high liquid absorption rate—through a simple structural design of high-density base paper and intermittent hydrophilic adhesive bonding. This is significantly superior to existing technologies such as integral coating and high-low density layered coating, and has outstanding industrialization and application value. Attached Figure Description

[0040] Figure 1 This is a 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.

[0041] Figure 2 This is a schematic diagram of adhesive dots on the surface of the composite diaphragm, where 4 is the unadhesive area on the surface of the base paper and 5 is the adhesive area on the surface of the base paper. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0043] Example 1

[0044] Preparation of base paper: Wood pulp is beating using a disc mill to a beating degree of 95°SR. After beating, the wood pulp is formed using a wire forming process with a forming concentration of 0.5%. After forming, it is pressed, dried, and wound to obtain base paper A with a thickness of 15.0μm.

[0045] Preparation of double-layer composite paper: Base paper A is divided into two rolls. Both rolls 1 and 2 are coated using gravure coating rollers. The gravure coating rollers have a circular groove pattern, with the area of ​​the circular grooves accounting for 30% of the effective area of ​​the gravure coating rollers. The coating solution is an aqueous solution of starch, with a temperature of 40℃ and a concentration of 5.0%. After coating, the adhesive content of the composite paper is 0.5 g / m². After coating, the starch-coated sides of rolls 1 and 2 are laminated together, then pressed, and then dried using eight drying cylinders at temperatures of 40℃, 45℃, 50℃, 60℃, 70℃, 80℃, 70℃, and 60℃. After drying, the paper is wound up and then slit to obtain a final product with a thickness of 30.5 μm (e.g., ...). Figure 1 , Figure 2 (As shown).

[0046] Example 2

[0047] Preparation of base paper: Wood pulp is beating using a disc mill to a beating degree of 95°SR. After beating, the wood pulp is formed into a wire mesh with a forming concentration of 0.5%. After forming, it is pressed, dried, and wound to obtain base paper A with a thickness of 20.0μm.

[0048] Preparation of double-layer composite paper: The base paper A is divided into two rolls. Both roll 1 and roll 2 are coated using gravure coating rollers. The pattern of the gravure coating rollers is a circular groove, and the area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating rollers. The coating solution is an aqueous solution of starch, the temperature of the coating solution is 40℃, the concentration of the coating solution is 6.0%, and the glue content of the composite paper after coating is 0.8g / m2. After coating, the starch solution-coated sides of roll 1 and roll 2 are laminated together, then pressed, and then dried using 8 drying cylinders at drying temperatures of 40℃, 45℃, 50℃, 60℃, 70℃, 80℃, 70℃, and 60℃, respectively. After drying, the paper is wound up and then slit to obtain a final product with a thickness of 40.8μm.

[0049] Example 3

[0050] Preparation of base paper: The hemp pulp was beating using a disc mill to a beating degree of 95°SR. After beating, the hemp pulp was formed using a wire forming process with a forming concentration of 0.5%. After forming, the pulp was pressed, dried, and wound to obtain base paper A with a thickness of 15.0 μm.

[0051] Preparation of double-layer composite paper: The base paper A is divided into two rolls. Both roll 1 and roll 2 are coated using gravure coating rollers. The pattern of the gravure coating rollers is a circular groove, and the area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating rollers. The coating solution is an aqueous solution of starch, the temperature of the coating solution is 40℃, the concentration of the coating solution is 5.0%, and the glue content of the composite paper after coating is 0.5g / m2. After coating, the starch solution-coated sides of roll 1 and roll 2 are laminated together, then pressed, and then dried using 8 drying cylinders at drying temperatures of 40℃, 45℃, 50℃, 60℃, 70℃, 80℃, 70℃, and 60℃ respectively. After drying, the paper is wound up and then slit to obtain a final product with a thickness of 30.5μm.

[0052] Example 4

[0053] Preparation of base paper: The hemp pulp was beating using a disc mill to a beating degree of 95°SR. After beating, the hemp pulp was formed using a wire forming process with a forming concentration of 0.5%. After forming, the pulp was pressed, dried, and wound to obtain base paper A with a thickness of 20.0 μm.

[0054] Preparation of double-layer composite paper: The base paper A is divided into two rolls. Both roll 1 and roll 2 are coated using gravure coating rollers. The pattern of the gravure coating rollers is a circular groove, and the area of ​​the circular groove accounts for 30% of the effective area of ​​the gravure coating rollers. The coating solution is an aqueous solution of starch, the temperature of the coating solution is 40℃, the concentration of the coating solution is 6.0%, and the glue content of the composite paper after coating is 0.8g / m2. After coating, the starch solution-coated sides of roll 1 and roll 2 are laminated together, then pressed, and then dried using 8 drying cylinders at drying temperatures of 40℃, 45℃, 50℃, 60℃, 70℃, 80℃, 70℃, and 60℃, respectively. After drying, the paper is wound up and then slit to obtain a final product with a thickness of 40.8μm.

[0055] Example 5

[0056] Similar to Example 1, the coating solution is a 5wt% PVA aqueous solution (degree of polymerization 1700±100, degree of hydrolysis 98%, temperature maintained at 40℃), and other technical features are the same as in Example 1.

[0057] Example 6

[0058] Similar to Example 1, the coating solution was a 4 wt% sodium polyacrylate solution (molecular weight ≈ 500,000, pH adjusted to 6.5), and other technical features were the same as in Example 1.

[0059] Example 7

[0060] Similar to Example 1, the dispensing liquid is as follows:

[0061] Main component: 5wt% starch aqueous solution;

[0062] Additives: 0.5wt% glutaraldehyde (based on dry starch);

[0063] Coating solution temperature: 40℃, stir well and react for 30 minutes;

[0064] Other technical features are the same as in Example 1.

[0065] Comparative Example 1

[0066] The wood pulp was pulped using a disc mill with a beating degree of 95.0°SR. After pulping, the wood pulp was formed using a long-net molding process with a molding concentration of 0.5%. After molding, it was pressed, dried, wound, and slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 15.0μm.

[0067] Comparative Example 2

[0068] The wood pulp was pulped using a disc mill with a beating degree of 94.5°SR. After pulping, the wood pulp was formed using a long-net molding process with a molding concentration of 0.5%. After molding, it was pressed, dried, rolled up, and slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 30.2μm.

[0069] Comparative Example 3

[0070] The wood pulp was pulped using a disc mill with a beating degree of 94.5°SR. After pulping, the wood pulp was formed using a long-net molding process with a molding concentration of 0.5%. After molding, it was pressed, dried, rolled up, and slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 40.1μm.

[0071] Comparative Example 4

[0072] The hemp pulp was beaten by a disc mill to a beating degree of 95.0°SR. After beating, the hemp pulp was formed into a long net. After forming, it was pressed, dried, rolled up, and cut to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 15.0μm.

[0073] Comparative Example 5

[0074] The hemp pulp was beaten by a disc mill to a beating degree of 94.5°SR. After beating, the hemp pulp was formed into a long net. After forming, it was pressed, dried, rolled up, and cut to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 30.2μm.

[0075] Comparative Example 6

[0076] The hemp pulp was pulped using a disc mill with a beating degree of 94.5°SR. After pulping, the hemp pulp was formed into a long net. After forming, it was pressed, dried, rolled up, and cut to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 40.3μm.

[0077] Comparative Example 7

[0078] The wood pulp was polished using a disc mill to achieve a freeness of 94.5°SR. After polishing, the wood pulp was formed using a long-wire forming process with a forming concentration of 0.5%. The cotton pulp was polished using a disc mill to achieve a freeness of 35°SR. After polishing, the cotton pulp was formed using a circular wire forming process with a forming concentration of 0.02%. The formed long-wire and circular wire layers were then laminated, followed by pressing, drying, winding, and slitting to obtain a high-voltage double-layer electrolytic capacitor separator with a thickness of 40.5 μm.

[0079] Comparative Example 8

[0080] Hemp pulp was beaten using a disc mill to a freeness of 94.5°SR. After beating, the hemp pulp was formed using a long-web forming process with a forming concentration of 0.5%. Cotton pulp was also beaten using a disc mill to a freeness of 35°SR. After beating, the cotton pulp was formed using a circular web forming process with a forming concentration of 0.02%. The formed long-web and circular web layers were then combined, followed by pressing, drying, winding, and slitting to obtain a high-voltage double-layer electrolytic capacitor diaphragm with a thickness of 40.5 μm.

[0081] Comparative Example 9

[0082] Similar to Example 1, two 15µm wood pulp base papers are bonded together with a continuous 10g / m² PVA coating with a thickness of 30.6µm. Other technical features are the same as in Example 1.

[0083] Comparative Example 10

[0084] Similar to Example 1, two 15µm wood pulp base papers are laminated with hydrophobic polyethylene wax-doped adhesive at 0.6g / m² (30% of area), resulting in a thickness of 30.5µm. Other technical features are the same as in Example 1.

[0085] Comparative Example 11

[0086] Similar to Example 1, the freeness of the two 15µm wood pulp base papers is 70 °SR, and the thickness is 30.4µm. Other technical features are the same as in Example 1.

[0087] Experimental Example 1

[0088] The process parameters and test results for four examples and eleven comparative examples are given below (as shown in Table 1). Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared by existing methods. The detection methods in the comparative examples and examples are as follows:

[0089] Tightness: GB / T451.3;

[0090] Thickness: GB / T451.3;

[0091] Breakdown voltage: GB / T12913;

[0092] Absorption height: GB / T461.1;

[0093] ESR: The diaphragm is fabricated into a capacitor, and the ESR is measured using an LCR meter at a temperature of 20°C and a frequency of 1 kHz.

[0094] Table 1 shows the process parameters and test results.

[0095]

[0096] Data Analysis:

[0097] 1. Breakdown voltage

[0098] Advantages in pressure resistance per unit thickness: Measured in “V / µm”, Examples 1–4 showed an improvement of 30–55% compared to the corresponding control, with the highest reaching 43–44 V / µm (Example 1, Comparative Example 10), demonstrating that localized hydrophilic dotting + composite structure significantly enhances the uniformity of the electric field and the strength of the fiber skeleton.

[0099] Comparison of continuous full-surface coating (Comparative Example 9): The thickness is similar to that of Example 1, but only 1150V, indicating that a large-area film will produce defect interfaces and weaken the electric field distribution.

[0100] 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 worse, verifying that "hydrophilicity" is the key to improving the overall performance.

[0101] 2. Liquid absorption performance (water absorption height in 10 minutes)

[0102] The water absorption height of high-density monolayer comparative examples 1–6 is only 2–3 mm; the water absorption height of wet-process stratified comparative examples 7 / 8 is slightly higher, up to 4 mm.

[0103] The liquid absorption height of the example is 58–87 mm, which is 20–30 times higher; this is due to the large number of interconnected pores retained between the base paper and the rapid capillary channels provided by the hydrophilic dispensing.

[0104] Comparative Example 9 (full-surface PVA) and Comparative Example 10 (hydrophobic wax dots) were only 6mm and 8mm respectively, further confirming that the synergistic effect of intermittent + hydrophilic is irreplaceable.

[0105] 3. Equivalent series resistance (ESR, 1kHz, 20℃)

[0106] The reduction in ESR is directly related to the amount of liquid absorbed: hydrophilic dispensing significantly increases the liquid content and shortens the ion migration path, thereby reducing impedance.

[0107] Even with higher breakdown voltages, Comparative Examples 9 and 10 still exhibited ESRs as high as 1.90Ω and 1.85Ω, respectively, failing to reach the level of the examples. This further demonstrates that relying solely on thick coatings or hydrophobic adhesives cannot achieve low ESR.

[0108] 4. Density and Structural Explanation

[0109] The compactness of both the examples and the monolayer high-density control remained at 0.90–0.92 g / cm³. -3 This demonstrates that the present invention achieves higher pressure resistance and liquid absorption through "hydrophilic intermittent dispensing + double-layer high-density base paper" without reducing density; the performance improvement does not come at the expense of a loose structure.

[0110] The layered wet web samples (Comparative Example 7 / Comparative Example 8) had significantly lower density (≈0.80 g / cm³). -3 Although the liquid absorption is slightly better than that of a single layer, the pressure resistance is significantly reduced, which proves that the low-density strategy cannot achieve a simultaneous improvement in both indicators.

[0111] 5. Conclusion

[0112] Optimal overall performance: The embodiment 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.

[0113] Experimental Example 2

[0114] Objective: To systematically verify that A) the polymer coating area accounts for 10%–40% of the effective paper surface area, and B) the polymer coating amount is 0.1 gm. -2 -10gm -2 The combined effects of these two process windows on diaphragm breakdown voltage, liquid absorption, and ESR.

[0115] 1. Test Plan

[0116]

[0117] Using L9(3) 2 Orthogonal array; the remaining conditions are completely consistent with those of Example 1 (15µm×2 starch dispensing, 8-segment gradient drying of gravure).

[0118] Three rolls of each sample were prepared, and the average value was taken from the test. The detection method was the same as that in the instruction manual—GB / T451.3, GB / T12913, GB / T461.1 and 1kHz ESR determination.

[0119] 2. Experimental Results (Average Values)

[0120]

[0121] 3. Range and Trend Analysis

[0122]

[0123] Breakdown voltage: It increases with the increase of coating area and amount of adhesive, but the growth curve tends to saturate; Factor A has a slightly stronger effect than Factor B.

[0124] Liquid absorption height: decreases significantly with excessive area or glue volume; the range indicates excessive glue application (10gm). -2 It has the most severe inhibition of liquid absorption.

[0125] ESR: The lowest value occurs when A=25% and B=1gm. -2 Excessive glue content caused the ESR to rise.

[0126] 4. Comprehensive evaluation (weighting method)

[0127] Let the breakdown voltage increase (+), water absorption increase (+), and ESR decrease (-); assign weights of 0.4:0.3:0.3 to calculate the overall score. The highest result is still group 5 (25% / 1gm). -2 ).

[0128] 5. Technical Effects

[0129] 1) If the coating area is less than 10%, the adhesion is insufficient and the breakdown voltage drops to below 1100V; if the coating area is 40%, the water absorption drops sharply to <15mm and the ESR is >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.

[0130] 2) Adhesive application amount <0.1gm -2 The composite material is prone to delamination; the adhesive application rate is 10gm. -2 When the pores are submerged, water absorption <10mm, ESR>2Ω; coating amount 0.1–10gm -2 It covers the feasible process band from "minimum adhesion requirements" to "critical pore sealing".

[0131] 3) Optimal combination (25% / 1gm) -2 The breakdown voltage reaches 1324V (55% higher than the 30µm monolayer reference), the water absorption is 62mm (20 times that of the 3mm reference), and the ESR is 1.48Ω (10% lower than the 1.65Ω reference of the monolayer), fully demonstrating the synergistic improvement of high pressure resistance, high liquid absorption, and low ESR.

[0132] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A high-voltage-resistant, high-absorbency composite electrolytic capacitor separator, characterized in that, The material comprises at least two layers of high-density electrolytic capacitor base paper, stacked sequentially along the thickness direction and then hot-pressed and dried. Each layer of base paper is obtained by wet forming, pressing, and drying of plant fibers with a freeness of 92°SR-98°SR. An adhesive layer is provided between adjacent base papers, and the following conditions are met: 1) The adhesive layer is composed of a hydrophilic polymer; 2) The adhesive layer is dispersed only on one side of at least one layer of base paper in a discontinuous, intermittent pattern, and the polymer coating area accounts for 10-40% of the effective area of ​​that side surface; 3) The amount of polymer applied is 0.1-10 g / m².

2. The diaphragm according to claim 1, characterized in that, The polymer is selected from 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 0.88-0.92 g / cm³.

4. The diaphragm according to claim 1, characterized in that, The adhesive layer pattern is a dotted or striped distribution formed by circular, striped, 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 1×10⁻⁶. 4 -2×10 5 .

6. The diaphragm according to claim 1, characterized in that, The polymer also contains 0.1-5 wt% of a crosslinking agent.

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

8. A method for preparing the diaphragm according to any one of claims 1-7, characterized in that, The method includes the following steps: 1) High-density base paper is obtained by pulping plant fibers with a freeness of 92°SR-98°SR and a pulp mass concentration of 0.3-0.7%, followed by wire forming, pressing and drying. 2) The base paper is intermittently coated with a hydrophilic polymer solution on one side 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℃. 3) Two or more sheets of base paper treated in step 2) are bonded together with the coated surfaces facing each other, and then dried and laminated by pressing and multi-stage heating cylinder at 30-90℃, controlling the amount of adhesive to be applied to be 0.1-10g / m², to obtain the target diaphragm.

9. The method according to claim 8, characterized in that, Step 2) Use a gravure coating roller with a circular groove on the surface, the groove area accounting 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 gradually decreased according to the direction of paper web movement; before lamination, a linear pressure of 0.1-1MPa is applied to enhance the bonding between the base papers.

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