High voltage resistant low loss electrolytic capacitor separator

Abstract

The utility model belongs to the field of paper for aluminum electrolytic capacitor, specifically relates to a kind of high voltage resistance low-loss electrolytic capacitor diaphragm and its preparation method. The diaphragm adopts plant fiber single-layer paper base, and the surface double side uses gravure coating to form the discontinuous point distribution hydrophilic polymer coating. The structure significantly reduces the smoothness of the diaphragm without significantly increasing the thickness, enhances the electrolyte adsorption, thereby reduces the ESR to 20-22 mΩ, while ensuring the breakdown voltage ≥550V. It is suitable for high-performance, small-sized aluminum electrolytic capacitor.

Description

Technical Field

[0001] This utility model belongs to the field of paper for aluminum electrolytic capacitors, specifically relating to a high voltage-resistant, low-loss 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] The separator in an electrolytic capacitor primarily functions to isolate the positive and negative electrodes and absorb the electrolyte. Based on application requirements, they can be categorized into high-voltage and low-voltage electrolytic capacitor separators. High-voltage electrolytic capacitor separators require high voltage withstand capability; low-voltage electrolytic capacitor separators have lower voltage withstand requirements but require good absorbency and a low equivalent series resistance (ESR). With technological advancements, even higher demands are placed on high-voltage electrolytic capacitor separators, requiring not only high voltage withstand capability but also low ESR. The quality of the separator's wettability with the electrolyte directly affects the capacitor's internal resistance; therefore, the most direct way to reduce the capacitor's ESR is to improve the separator's wettability with the electrolyte.

[0004] Typically, high-voltage electrolytic capacitor separators are made from plant fibers with a high degree of beating to ensure a dense separator and thus high voltage withstand performance. However, excessively high beating results in poor electrolyte absorption, reducing the amount of electrolyte adsorbed and ultimately leading to a high ESR. Chinese patent CN116479682A discloses a method for preparing composite electrolytic capacitor paper. This product improves the breakdown voltage of two or more layers of electrolytic paper by coating the surface with polyvinyl alcohol and glutaraldehyde. Although the breakdown voltage is significantly improved, the amount of electrolyte adsorbed is reduced because the spaces between the composite papers are filled with coatings, resulting in a still high ESR value.

[0005] Another mainstream strategy is to composite a high-density insulating wood pulp layer with a low-density cotton pulp or hemp pulp layer: the high-density layer ensures voltage resistance, while the low-density layer provides liquid absorption voids. Chinese patent CN204753253U discloses a high-voltage resistant electrolytic capacitor paper and its preparation method. This product is obtained by compositing low-density cotton pulp and / or hemp pulp with high-density insulating wood pulp and then coating it. Due to the presence of a low-density layer, the product's voltage resistance is difficult to achieve at the same thickness. Patent CN201810006288.1 discloses a voltage-resistant electrolytic capacitor paper and its preparation method. This product is obtained by compositing low-density sisal pulp with high-density sisal pulp and then coating it. Also containing a low-density layer, the product's voltage resistance is also difficult to achieve at the same thickness.

[0006] Chinese patent CN109722945B discloses a breakdown-resistant composite electrolytic capacitor paper and its production method. The product consists of a pressure-resistant layer and an absorbent layer. The pressure-resistant layer pulp includes insulating wood pulp and nanocellulose, and the absorbent layer pulp includes hemp pulp, cotton pulp and straw pulp. The pressure-resistant layer and the absorbent layer are then composited through a long cylindrical wire to obtain the final product. However, because the product also contains a low-density layer, the pressure resistance per unit thickness is still not high.

[0007] Currently, high-voltage electrolytic capacitor separators, due to their high degree of beating and the need for calendering, have extremely smooth surfaces. After being fabricated into capacitors, they are tightly bonded to aluminum foil, resulting in very few pores between the separator and the aluminum foil. This reduces the amount and rate of electrolyte adsorption, leading to a higher ESR in the capacitor. To reduce ESR, a layer of low-density fiber material is usually laminated onto the surface of the high-pressure paper. While this increases the amount of electrolyte adsorption, it significantly increases the separator thickness, which is detrimental to the miniaturization of capacitors. Summary of the Invention

[0008] To overcome the shortcomings of existing electrolytic capacitor separators in that they cannot simultaneously satisfy both high breakdown voltage and low ESR, this invention provides a high voltage withstand and low loss electrolytic capacitor separator that, while ensuring high voltage withstand, also ensures a low separator thickness and significantly reduces the ESR value of the capacitor after it is fabricated.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A high-voltage-resistant, low-loss electrolytic capacitor separator, the separator comprising: Single-layer high-density paper base made of plant fibers. A hydrophilic polymer coating is formed on the A and B sides of the paper substrate, respectively. The coating is uniformly dispersed on the A and B sides of the paper substrate only in a discontinuous intermittent pattern.

[0010] Preferably, the single-layer high-density paper base is made of plant fibers with a beating degree of 90°SR-98°SR and a paper base density of ≥ 0.85 g / cm³.

[0011] Preferably, the density of each base paper is 0.88-0.92 g / cm³, and can be selected as 0.88, 0.89, 0.90, 0.91, or 0.92 g / cm³.

[0012] Preferably, the coating has a coverage of 20%-70% on any side, and the total coating amount is 0.2-6.0 g / m².

[0013] Preferably, the coating has a coverage of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70% on any side.

[0014] Preferably, the total adhesive application 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, or 6.0g / m².

[0015] The coating pattern is a dotted or striped distribution formed by circular, striped, or polygonal grooves.

[0016] 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.

[0017] Preferably, the polymer is starch or polyvinyl alcohol, and its number average molecular weight is 1×10⁻⁶. 4 -2×10 5 .

[0018] Preferably, the plant fiber is wood pulp, hemp pulp, or a combination thereof.

[0019] Preferably, the diaphragm thickness is ≤ 30 µm, the breakdown voltage is ≥ 550 V, and the equivalent series resistance (ESR) measured at 1 kHz and 20 °C is ≤ 22 mΩ.

[0020] Preferably, the diaphragm has a thickness of 15-25 μm and a smoothness of 40-60 S.

[0021] Preferably, the coating is applied using gravure coating, and the surface of the gravure coating roller is a circular groove with the groove area accounting for 20-70% of the roller surface.

[0022] This invention, by employing the aforementioned technical solution, significantly reduces the surface smoothness of the separator after coating the surface with a hydrophilic polymer. It also effectively increases the porosity between the separator and the aluminum foil, enhancing the adsorption of electrolyte and significantly reducing the capacitor's ESR. Furthermore, since the thickness remains largely unchanged after coating with the polymer material, this invention is particularly suitable for preparing thin high-voltage electrolytic capacitor separators requiring a thickness of less than 30 μm. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of adhesive dots on the diaphragm surface, where 1 is the unadhesive area on the surface of the base paper, and 2 is the adhesive area on the surface of the base paper. Detailed Implementation

[0024] The technical solutions in the embodiments of this utility model will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0025] Example 1 Preparation of base paper: Wood pulp is beating using a disc mill to a beating degree of 96.0°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 Y1 with a thickness of 15.0μm.

[0026] Paper preparation: Side A of the base paper Y1 is coated using a gravure coating roller. The gravure coating roller has a circular groove pattern, and the area of ​​the circular groove accounts for 40% of the effective area of ​​the gravure coating roller. The polymer solution used for coating is an aqueous solution of hydroxypropyl cellulose, and the holding temperature of the polymer solution is 40℃ with a concentration of 4.0%. After coating, it is dried in three drying cylinders at temperatures of 60℃, 70℃, and 80℃ respectively. After drying, side B of the base paper Y1 is then coated using a gravure coating roller. The total sizing amount after double-sided coating is 0.4 g / m². 2 After coating side B, the material is dried in six drying cylinders at temperatures of 60℃, 60℃, 70℃, 80℃, 80℃, and 70℃ respectively. After drying, it is wound up to obtain a final product with a thickness of 15.2μm (e.g., ...). Figure 1 ).

[0027] Example 2 Preparation of base paper: Wood pulp is beating using a disc mill to a beating degree of 96.0°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 Y1 with a thickness of 15.0μm.

[0028] Paper preparation: Side A of the base paper Y1 is coated using a gravure coating roller. The gravure coating roller has a circular groove pattern, and the area of ​​the circular groove accounts for 60% of the effective area of ​​the gravure coating roller. The polymer solution used for coating is an aqueous solution of hydroxypropyl cellulose, with a holding temperature of 40℃ and a concentration of 4.0%. After coating, it is dried in three drying cylinders at temperatures of 60℃, 70℃, and 80℃ respectively. After drying, side B of the base paper Y1 is then coated using a gravure coating roller. The total sizing amount after double-sided coating is 2.5 g / m². 2 After coating the B side, it is dried in 6 drying cylinders at temperatures of 60℃, 60℃, 70℃, 80℃, 80℃ and 70℃ respectively. After drying, it is rolled up to obtain a final product with a thickness of 15.5μm.

[0029] Example 3 Preparation of base paper: Wood pulp is beating using a disc mill to a beating degree of 95.0°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 Y1 with a thickness of 20.2μm.

[0030] Paper preparation: Side A of the base paper Y1 is coated using a gravure coating roller. The gravure coating roller has a circular groove pattern, and the area of ​​the circular groove accounts for 60% of the effective area of ​​the gravure coating roller. The polymer solution used for coating is an aqueous solution of hydroxypropyl cellulose, and the holding temperature of the polymer solution is 40℃ with a concentration of 4.0%. After coating, it is dried in three drying cylinders at temperatures of 60℃, 70℃, and 80℃ respectively. After drying, side B of the base paper Y1 is then coated using a gravure coating roller. The total sizing amount after double-sided coating is 2.1 g / m². 2 After coating the B side, it is dried in 6 drying cylinders at temperatures of 60℃, 60℃, 70℃, 80℃, 80℃ and 70℃ respectively. After drying, it is rolled up to obtain a final product with a thickness of 20.5μm.

[0031] Example 4 Preparation of base paper: The hemp pulp was beating using a disc mill to a beating degree of 96.0°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 Y1 with a thickness of 15.0μm.

[0032] Paper preparation: Side A of the base paper Y1 is coated using a gravure coating roller. The gravure coating roller has a circular groove pattern, and the area of ​​the circular groove accounts for 40% of the effective area of ​​the gravure coating roller. The polymer solution used for coating is an aqueous solution of hydroxypropyl cellulose, and the holding temperature of the polymer solution is 40℃ with a concentration of 4.0%. After coating, it is dried in three drying cylinders at temperatures of 60℃, 70℃, and 80℃ respectively. After drying, side B of the base paper Y1 is then coated using a gravure coating roller. The total sizing amount after double-sided coating is 0.4 g / m². 2After coating the B side, the product is dried in six drying cylinders at temperatures of 60℃, 60℃, 70℃, 80℃, 80℃, and 70℃. After drying, the product is rolled up to obtain a final product with a thickness of 15.1μm.

[0033] Example 5 Preparation of base paper: The hemp pulp was beating using a disc mill to a beating degree of 96.0°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 Y1 with a thickness of 15.0μm.

[0034] Paper preparation: Side A of the base paper Y1 is coated using a gravure coating roller. The gravure coating roller has a circular groove pattern, and the area of ​​the circular groove accounts for 50% of the effective area of ​​the gravure coating roller. The polymer solution used for coating is an aqueous solution of hydroxypropyl cellulose, with a holding temperature of 40℃ and a concentration of 4.0%. After coating, it is dried in three drying cylinders at temperatures of 60℃, 70℃, and 80℃ respectively. After drying, side B of the base paper Y1 is then coated using a gravure coating roller. The total sizing amount after double-sided coating is 1.9 g / m². 2 After coating the B side, it is dried in 6 drying cylinders at temperatures of 60℃, 60℃, 70℃, 80℃, 80℃ and 70℃ respectively. After drying, it is rolled up to obtain a final product with a thickness of 15.3μm.

[0035] Example 6 Preparation of base paper: The hemp pulp was beating using a disc mill to a beating degree of 95.0°SR. After beating, the hemp pulp was formed using a wire forming process with a forming concentration of 0.5%. After forming, the base paper Y1 with a thickness of 20.3μm was obtained by pressing, drying, and winding.

[0036] Paper preparation: Side A of the base paper Y1 is coated using a gravure coating roller. The gravure coating roller has a circular groove pattern, and the area of ​​the circular groove accounts for 60% of the effective area of ​​the gravure coating roller. The polymer solution used for coating is an aqueous solution of hydroxypropyl cellulose, with a holding temperature of 40℃ and a concentration of 4.0%. After coating, it is dried in three drying cylinders at temperatures of 60℃, 70℃, and 80℃ respectively. After drying, side B of the base paper Y1 is then coated using a gravure coating roller. The total sizing amount after double-sided coating is 1.9 g / m². 2 After coating the B side, it is dried in 6 drying cylinders at temperatures of 60℃, 60℃, 70℃, 80℃, 80℃ and 70℃ respectively. After drying, it is rolled up to obtain a final product with a thickness of 20.6μm.

[0037] Example 7 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.

[0038] Example 8 Similar to Example 1, the coating liquid is a 4wt% starch solution, and other technical features are the same as in Example 1.

[0039] Comparative Example 1 The wood pulp was beating using a disc mill with a beating degree of 96.0°SR. After beating, 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 15.0μm.

[0040] Comparative Example 2 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, rolled up, and slit to obtain a high-voltage single-layer electrolytic capacitor diaphragm with a thickness of 20.2μm.

[0041] Comparative Example 3 The hemp pulp was pulped using a disc mill with a beating degree of 96.0°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 15.0μm.

[0042] Comparative Example 4 The hemp pulp was pulped using a disc mill with a beating degree of 95.0°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 20.3μm.

[0043] Comparative Example 5 Similar to Example 1, the area of ​​the circular groove accounts for 10% of the effective area of ​​the gravure coating roller, and other technical features are the same as in Example 1.

[0044] Comparative Example 6 Similar to Example 1, the area of ​​the circular groove accounts for 90% of the effective area of ​​the gravure coating roller, and other technical features are the same as in Example 1.

[0045] Comparative Example 7 Similar to Example 1, side A of the base paper Y1 is coated, while side B is not coated. Other technical features are the same as in Example 1.

[0046] Comparative Example 8 Similar to Example 1, both sides of the base paper are coated with a continuous aqueous solution of hydroxypropyl cellulose, and other technical features are the same as in Example 1.

[0047] Comparative Example 9 Similar to Example 1, both sides of the base paper are coated with hydrophobic polyethylene wax dots, and other technical features are the same as in Example 1.

[0048] Experimental Example 1 The process parameters and test results of the embodiments and comparative examples of this utility model are given below (as shown in Table 1). Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this utility model can be purchased from the market or prepared by existing methods. The detection methods in the above comparative examples and embodiments are as follows: Tightness: GB / T 451.3; Thickness: GB / T 451.3; Breakdown voltage: GB / T 12913; Smoothness: GB / T 456; 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.

[0049] Table 1 shows the process parameters and test results. The above 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 present 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, low-loss electrolytic capacitor separator, characterized in that, The diaphragm includes: Single-layer high-density paper base made of plant fibers. A hydrophilic polymer coating is formed on the A and B sides of the paper substrate, respectively. The coating is uniformly dispersed on the A and B sides of the paper substrate only in a discontinuous intermittent pattern.

2. The diaphragm according to claim 1, characterized in that, The single-layer high-density paper base is made of plant fibers with a beating degree of 90°SR-98°SR and a paper base density of ≥ 0.85 g / cm³.

3. The diaphragm according to claim 1, characterized in that, The coating coverage on any side is 20%-70%, and the total coating amount is 0.2-6.0 g / m².

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

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

7. The diaphragm according to claim 1, characterized in that, The plant fiber is wood pulp or hemp pulp.

8. The diaphragm according to claim 1, characterized in that, The diaphragm thickness is ≤ 30 µm, the breakdown voltage is ≥ 550 V, and the equivalent series resistance (ESR) measured at 1 kHz and 20 ℃ is ≤ 22 mΩ.

9. The diaphragm according to claim 1, characterized in that, The diaphragm has a thickness of 15-25 μm and a smoothness of 40-60 S.

10. The diaphragm according to claim 1, characterized in that, The coating is applied using gravure printing, and the surface of the gravure printing roller has circular grooves, with the groove area accounting for 20-70% of the roller surface.

Images