Electrolytic paper for aluminum electrolytic capacitors and its preparation method

Abstract

An electrolytic paper for aluminum electrolytic capacitors includes an upper surface layer, an intermediate support layer, and a lower surface layer. Both the upper and lower surface layers comprise cotton pulp fibers and / or hemp pulp fibers, while the intermediate support layer comprises aramid fibers. An interpenetrating polymer network is formed between the upper and lower surface layers and the intermediate support layer using active functional groups of polyacrylic acid or polyglycidyl methacrylate and its derivatives. In this invention, the intermediate support layer exhibits extremely high insulation strength and thermal stability, resulting in a 30%-50% or higher breakdown voltage of the composite electrolytic paper compared to pure natural fiber electrolytic paper of the same basis weight, demonstrating superior voltage withstand performance. Furthermore, the interpenetrating polymer network formed between the upper and lower surface layers and the intermediate support layer using polyacrylic acid or polyglycidyl methacrylate and its derivatives ensures rapid and thorough wetting of the electrolyte and long-term electrolyte retention, thereby ensuring capacitor capacity and reducing ESR.

Description

Technical Field

[0001] This invention relates to an electrolytic paper for aluminum electrolytic capacitors, and more particularly to a three-layer composite electrolytic paper for high-voltage aluminum electrolytic capacitors and its preparation method. Background Technology

[0002] Aluminum electrolytic capacitors are widely used in consumer electronics, industrial power supplies, new energy, and automotive electronics due to their advantages such as large capacitance per unit volume and high cost-effectiveness. The electrolytic paper, as the core inner insulating medium of the capacitor, directly determines the capacitor's voltage withstand capability, losses, lifespan, and reliability.

[0003] As electronic devices develop towards higher voltage, higher power, and smaller size, the voltage withstand requirements for aluminum electrolytic capacitors are increasing. Traditional electrolytic paper is mostly made from natural fibers (such as wood pulp and hemp pulp). Its advantage is good wettability with electrolyte, but the fibers are relatively coarse and the pores are uneven, making them prone to local breakdown under high electric fields, thus creating a bottleneck in improving voltage withstand. Paper made from pure chemical fibers (such as aramid) has extremely high thermal stability and mechanical strength, but it is expensive and has relatively poor affinity and electrolyte retention, making its performance unsatisfactory when used alone.

[0004] Therefore, how to balance excellent high-voltage resistance, good electrolyte wettability, and reasonable cost has become a technical problem that urgently needs to be solved in this field.

[0005] To address the above issues, patent CN109577102A discloses an electrolytic capacitor paper and its preparation method. This electrolytic paper employs a three-layer structure; however, it has two high-voltage-resistant fiber layers, which severely affects the electrolyte impregnation efficiency. Furthermore, the three layers are bonded together using PVA, and after the PVA film forms, its electrolyte retention is further reduced, impacting the lifespan of the aluminum electrolytic capacitor. Additionally, the presence of PVA between the high-voltage-resistant fiber layer and the nanofiber layer leads to a higher equivalent ESR value in the product. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide an electrolytic paper for aluminum electrolytic capacitors with a three-layer structure and a method for preparing the same.

[0007] To solve the above-mentioned technical problems, the technical solution proposed by the present invention is as follows: an electrolytic paper for aluminum electrolytic capacitors, characterized in that: it includes an upper surface layer, an intermediate support layer and a lower surface layer, wherein the upper surface layer and the lower surface layer both include cotton pulp fiber and / or hemp pulp fiber, and the intermediate support layer includes aramid fiber; the upper surface layer and the lower surface layer and the intermediate support layer are connected by an interpenetrating polymer network formed by active functional groups of polyacrylic acid or polyglycidyl methacrylate and its derivatives.

[0008] Preferably, in the above-mentioned electrolytic paper for aluminum electrolytic capacitors, the upper surface layer accounts for 20%-40% of the total weight of the electrolytic paper; the intermediate support layer accounts for 30%-70% of the total weight of the electrolytic paper; and the lower surface layer accounts for 20%-40% of the total weight of the electrolytic paper.

[0009] Preferably, in the above-mentioned electrolytic paper for aluminum electrolytic capacitors, the beating degree of the upper and lower surface layers is between 25-40°SR; and the beating degree of the intermediate support layer is between 15-30°SR.

[0010] Preferably, in the above-mentioned electrolytic paper for aluminum electrolytic capacitors, the intermediate support layer further includes one or more of polyester fiber and ultrafine glass fiber.

[0011] A method for preparing electrolytic paper for aluminum electrolytic capacitors includes the following steps:

[0012] 1) Beat cotton pulp or hemp pulp in water to form natural fiber pulp, and set aside; the freeness should be between 25-40°SR;

[0013] 2) Pulp the aramid fibers in a dispersant to form a chemical fiber slurry, and set aside for use; the freeness should be between 15-30°SR.

[0014] 3) Prepare solutions of one or more monomers of acrylic acid or glycidyl methacrylate and their derivatives;

[0015] 4) Use a slanted wire or cylinder paper machine with three headboxes; introduce the prepared natural fiber pulp into the upper headbox and lower headbox respectively, and introduce the chemical fiber pulp into the middle headbox; the three pulps are simultaneously fed onto the wire, and the monomer solution prepared in step 3) is sprayed onto the surface of the wet intermediate support layer flowing out of the middle headbox; then the upper and lower surface layers flowing out of the upper and lower headboxes are interwoven and compounded in a wet state to form a wet paper web;

[0016] 5) Pressing:

[0017] The composite wet paper web is further dehydrated through the press section;

[0018] 6) After pressing, the composite wet paper web is polymerized at a temperature of room temperature to -80℃;

[0019] 7) Enter the drying section for drying, and the drying temperature shall not exceed 200℃.

[0020] In the above-mentioned method for preparing electrolytic paper for aluminum electrolytic capacitors, preferably, in step 3), an initiator is added to the monomer solution, and the weight of the initiator is 0.1%-0.5% of the weight of the monomer in the monomer solution; the initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, or tert-butyl hydroperoxide + ascorbic acid.

[0021] In the above-mentioned method for preparing electrolytic paper for aluminum electrolytic capacitors, preferably, the dispersant of the chemical fiber slurry includes one or more of nano-silica, graphene oxide, poly(N-isopropylacrylamide), polyacrylic acid, and polyvinylpyrrolidone.

[0022] In the above-mentioned method for preparing electrolytic paper for aluminum electrolytic capacitors, preferably, the solvent in the monomer solution in step 3) is a mixed solvent of ethylene glycol and water, and the weight concentration of the monomer is 5%-15%.

[0023] In the preferred method for preparing electrolytic paper for aluminum electrolytic capacitors described above, after step 6) is completed, the electrolytic paper is immersed in an ethylene glycol solution to wash away oligomers and unreacted monomers.

[0024] Compared with existing technologies, the advantages of this invention are as follows: In this invention, the high-strength chemical fibers such as aramid in the intermediate support layer have extremely high insulation strength and thermal stability, forming a robust "insulating wall" that effectively blocks the formation of conductive channels, increasing the breakdown voltage (BDV) of the composite electrolytic paper by 30%-50% or more compared to pure natural fiber electrolytic paper of the same basis weight; demonstrating excellent voltage resistance. The intermediate support layer also enhances the tensile strength of the electrolytic paper, making it less prone to breakage and fuzzing during high-speed winding. Furthermore, in this invention, the upper and lower surface layers are made of natural fibers, and an interpenetrating polymer network of polyacrylic acid or polyglycidyl methacrylate and its derivatives is formed between the upper and lower surface layers and the intermediate support layer, ensuring rapid and sufficient wetting of the electrolyte and long-term electrolyte retention capacity of the electrolytic paper as a whole, thus ensuring capacitor capacity and reducing ESR. Detailed Implementation

[0025] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0026] It should be noted that when a component is described as being "fixed to, attached to, connected to or connected to" another component, it can be directly fixed to, attached to, connected to or connected to the other component, or it can be indirectly fixed to, attached to, connected to or connected to the other component through other intermediate connectors.

[0027] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0028] Example 1

[0029] An electrolytic paper for aluminum electrolytic capacitors includes an upper surface layer, an intermediate support layer, and a lower surface layer. The upper surface layer accounts for 20%-40% of the total weight of the electrolytic paper; the intermediate support layer accounts for 30%-70% of the total weight of the electrolytic paper; and the lower surface layer accounts for 20%-40% of the total weight of the electrolytic paper. The freeness of the upper and lower surface layers is between 25-40°SR; the freeness of the intermediate support layer is between 15-30°SR.

[0030] In this embodiment, both the upper and lower surface layers comprise cotton pulp fibers and / or hemp pulp fibers, and the intermediate support layer is aramid fiber; an electrolytic paper for aluminum electrolytic capacitors is characterized by comprising an upper surface layer, an intermediate support layer, and a lower surface layer, wherein both the upper and lower surface layers comprise cotton pulp fibers and / or hemp pulp fibers, and the intermediate support layer comprises aramid fiber; the upper and lower surface layers and the intermediate support layer are connected by an interpenetrating polymer network formed by active functional groups of polyacrylic acid or polyglycidyl methacrylate and its derivatives.

[0031] In this embodiment, the intermediate support layer needs to be formed by pulping aramid fibers because the surface of the wet aramid fiber paper formed after pulping contains abundant microfibers and voids. Simultaneously, the wet natural fiber paper formed after pulping cotton pulp and / or hemp pulp also contains abundant microfibers and voids. This facilitates the penetration of polyacrylic acid or polyglycidyl methacrylate and its derivatives. After polymerization, the formed polymer forms a network structure, which interpenetrates with the microfibers of the fibers on both sides, forming an interpenetrating polymer network. Simultaneously, the carboxyl groups on the polyacrylic acid or polyglycidyl methacrylate and its derivatives undergo esterification with the hydroxyl groups on the surface of the natural fiber paper formed from cotton pulp and / or hemp pulp, forming ester bonds. Through these two effects, a continuous transition layer is formed between the intermediate support layer and the upper and lower surface layers, effectively enhancing the connection strength between the intermediate support layer and the upper and lower surface layers.

[0032] In this embodiment, the carboxyl groups on polyacrylic acid or polyglycidyl methacrylate and their derivatives have electrolyte-loving properties, attracting the electrolyte to distribute evenly. This reduces the ESR value of the product after forming the aluminum electrolytic capacitor. Simultaneously, the uniform electrolyte ensures a relatively uniform electric field distribution within the core package, preventing excessive voltage stress in low-liquid areas from breaking down the oxide film, and also avoiding uneven mechanical stress in high-liquid areas due to excessive pressure. The action of polyacrylic acid or polyglycidyl methacrylate and their derivatives can increase the electrolyte absorption rate of the electrolytic paper by 15-30%, and make the absorption rate more uniform.

[0033] In this embodiment, a method for preparing electrolytic paper for aluminum electrolytic capacitors is also provided, comprising the following steps:

[0034] 1) Beat cotton pulp or hemp pulp in water to form natural fiber pulp, and set aside; the beating degree should be between 25-40°SR.

[0035] 2) Pulp the aramid fibers in a dispersant to form a chemical fiber slurry, and set aside for use; the freeness is between 15-30°SR; the dispersant for the chemical fiber slurry includes one or more of nano silica, graphene oxide, poly(N-isopropylacrylamide), polyacrylic acid, and polyvinylpyrrolidone.

[0036] 3) Prepare a monomer solution of one or more of acrylic acid or glycidyl methacrylate and their derivatives; the solvent in the monomer solution is a mixture of ethylene glycol and water, and the weight concentration of the monomer is 5%-15%. In this embodiment, the weight ratio of ethylene glycol to water is 3:7.

[0037] 4) Use a slanted wire or cylinder paper machine with three headboxes; introduce the prepared natural fiber pulp into the upper headbox and lower headbox respectively, and introduce the chemical fiber pulp into the middle headbox; the three pulps are simultaneously fed onto the wire, and the monomer solution prepared in step 3) is sprayed onto the surface of the wet intermediate support layer flowing out of the middle headbox; then the upper and lower surface layers flowing out of the upper and lower headboxes are interwoven and compounded in a wet state to form a wet paper web.

[0038] 5) Pressing: The composite wet paper web is further dehydrated through the pressing section.

[0039] 6) After pressing, the composite wet paper web is polymerized at a temperature of room temperature to 80°C; after completion, the electrolytic paper is immersed in an ethylene glycol solution to wash away oligomers and unreacted monomers.

[0040] 7) Enter the drying section for drying, and the drying temperature shall not exceed 200℃.

[0041] In this embodiment, in step 3), an initiator is added to the monomer solution. The weight of the initiator is 0.1%-0.5% of the monomer weight in the monomer solution. The initiator includes azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (AIHHNnitrile), or tert-butyl hydroperoxide + ascorbic acid. Azobisisobutyronitrile has a decomposition temperature of 50-70℃, suitable for low-temperature polymerization to avoid damage to the kapok fiber, and its decomposition products are tetramethylsuccinate and nitrogen. Azobisisoheptanenitrile has a decomposition temperature of 40-60℃, and its decomposition products are also nitrogen and organic nitriles. Neither of these two initiators produces ions harmful to the electrolyte. Tert-butyl hydroperoxide + ascorbic acid can initiate polymerization at room temperature to 40℃, with ascorbic acid as the reducing agent, and its decomposition products are tert-butanol, etc., which is relatively friendly to the electrolyte system.

[0042] In this embodiment, the intermediate support layer, composed of high-strength chemical fibers such as aramid, possesses extremely high insulation strength and thermal stability, forming a robust "insulating wall" that effectively blocks the formation of conductive channels. This results in a 30%-50% increase in breakdown voltage of the composite electrolytic paper compared to electrolytic paper made from pure natural fibers of the same basis weight, demonstrating superior voltage resistance. The intermediate support layer also enhances the tensile strength of the electrolytic paper, making it less prone to breakage and fuzzing during high-speed winding. Furthermore, in this invention, the upper and lower surface layers are made of natural fibers, and an interpenetrating polymer network of polyacrylic acid or polyglycidyl methacrylate and its derivatives is formed between the upper and lower surface layers and the intermediate support layer. This ensures rapid and complete wetting of the electrolyte and long-term electrolyte retention, guaranteeing capacitor capacity and reducing ESR.

[0043] Example 2

[0044] In this embodiment, polyester fibers are added to the intermediate support layer, and the weight of the polyester fibers is 5%-30% of the weight of the aramid fibers. The other parts of this embodiment are the same as those in Embodiment 1.

[0045] Example 3

[0046] In this embodiment, ultrafine glass fibers are added to the intermediate support layer, and the weight of the ultrafine glass fibers is 5%-30% of the weight of the aramid fibers. The other parts of this embodiment are the same as those in Embodiment 1.

[0047] Comparative Example 1

[0048] In Comparative Example 1, the upper and lower surface layers were not bonded to the intermediate support layer using an interpenetrating polymer network formed by active functional groups of polyacrylic acid or polyglycidyl methacrylate and its derivatives; instead, they were directly physically bonded. Specifically, a slanted wire or cylinder paper machine with three headboxes was used; the prepared natural fiber pulp was introduced into the upper and lower headboxes respectively, and the chemical fiber pulp was introduced into the middle headbox; the three pulps were simultaneously fed onto the wire; then the upper and lower surface layers flowing out of the upper and lower headboxes were interwoven and bonded in a wet state to form a wet paper web.

[0049] The rest is the same as in Example 1.

[0050] The breakdown voltage, tensile strength, and electrolyte wetting rate of the electrolytic paper from Examples 1, 2, 3, and Comparative Example 1 were tested respectively; the results are shown in the table below:

[0051] Serial Number Breakdown voltage (V) Longitudinal tensile strength (kN / m) Electrolyte wetting rate (complete wetting time) (s) Example 1 1859 7.3 7.8 Example 2 1863 7.6 7.8 Example 3 1867 7.6 7.9 Comparative Example 1 1504 6.5 10.1

[0052] The electrolytic papers from Examples 1, 2, 3, and Comparative Example 1 were used to prepare 400V, 180μF liquid aluminum electrolytic capacitors. Except for the electrolytic paper, all other components were identical. Ten samples were taken from each example, and their average ESR, leakage current, and loss were tested. The results are shown in the table below.

[0053] Serial Number ESR (Ω) Leakage current (μA) loss(%) Example 1 0.199801 7.65 3.679 Example 2 0.21591 9.43 3.782 Example 3 0.217114 8.23 3.913 Comparative Example 1 1.79866 35.05 5.341

[0054] .

Claims

1. An electrolytic paper for aluminum electrolytic capacitors, characterized in that: It includes an upper surface layer, an intermediate support layer and a lower surface layer. The upper surface layer and the lower surface layer both include cotton pulp fiber and / or hemp pulp fiber. The intermediate support layer includes aramid fiber. The upper surface layer, the lower surface layer and the intermediate support layer are connected to each other by an interpenetrating polymer network formed by polyacrylic acid or polyglycidyl methacrylate and its derivatives.

2. The electrolytic paper for aluminum electrolytic capacitors according to claim 1, characterized in that: The upper surface layer accounts for 20%-40% of the total weight of the electrolytic paper; the middle support layer accounts for 30%-70% of the total weight of the electrolytic paper; and the lower surface layer accounts for 20%-40% of the total weight of the electrolytic paper.

3. The electrolytic paper for aluminum electrolytic capacitors according to claim 1, characterized in that: The beating degree of the upper and lower surface layers is between 25-40°SR; the beating degree of the intermediate support layer is between 15-30°SR.

4. The electrolytic paper for aluminum electrolytic capacitors according to claim 1, characterized in that: The intermediate support layer also includes one or more of polyester fibers and ultrafine glass fibers.

5. A method for preparing electrolytic paper for aluminum electrolytic capacitors, characterized in that, Includes the following steps: 1) Pulp cotton pulp or hemp pulp in water to form a natural fiber pulp, and set aside for later use; The freeness is between 25-40°SR; 2) Pulp the aramid fibers in a dispersant to form a chemical fiber slurry, and set aside for use; the freeness should be between 15-30°SR. 3) Prepare solutions of one or more monomers of acrylic acid or glycidyl methacrylate and their derivatives; 4) Use a slanted wire or cylinder paper machine with three headboxes; introduce the prepared natural fiber pulp into the upper headbox and lower headbox respectively, and introduce the chemical fiber pulp into the middle headbox; the three pulps are simultaneously fed onto the wire, and the monomer solution prepared in step 3) is sprayed onto the surface of the wet intermediate support layer flowing out of the middle headbox; then the upper and lower surface layers flowing out of the upper and lower headboxes are interwoven and compounded in a wet state to form a wet paper web; 5) Pressing: The composite wet paper web is further dehydrated through the press section; 6) After pressing, the composite wet paper web is kept at a temperature of room temperature to 80℃ for polymerization; 7) Enter the drying section for drying, and the drying temperature shall not exceed 200℃.

6. The method for preparing electrolytic paper for aluminum electrolytic capacitors according to claim 5, characterized in that: In step 3), an initiator is added to the monomer solution, and the weight of the initiator is 0.1%-0.5% of the weight of the monomer in the monomer solution; the initiator includes azobisisobutyronitrile, azobisisoheptanenitrile, or tert-butyl hydroperoxide + ascorbic acid.

7. The method for preparing electrolytic paper for aluminum electrolytic capacitors according to claim 5, characterized in that: The dispersant of the chemical fiber pulp includes one or more of nano-silica, graphene oxide, poly(N-isopropylacrylamide), polyacrylic acid, and polyvinylpyrrolidone.

8. The method for preparing electrolytic paper for aluminum electrolytic capacitors according to claim 5, characterized in that: In step 3), the solvent in the monomer solution is a mixture of ethylene glycol and water, and the weight concentration of the monomer is 5%-15%.

9. The method for preparing electrolytic paper for aluminum electrolytic capacitors according to claim 5, characterized in that: After step 6) is completed, immerse the electrolytic paper in the ethylene glycol solution to wash away the oligomers and unreacted monomers.