A method for preparing a high-liquid-absorption electrolytic capacitor paper

Abstract

The application discloses a preparation method of high-liquid-absorption electrolytic capacitor paper. First, coniferous wood pulp is prepared into pulp, and then oxygen in the pulp is removed; an initiator is added into the pulp, and after uniform stirring, a fiber modification reagent is added, and after reaction, modified pulp is obtained; the pulp is washed thoroughly, and then wet papermaking is performed, so that the high-liquid-absorption electrolytic capacitor paper is obtained, wherein the fiber modification reagent is selected from one or more of N,N-dimethyl acrylamide, dimethylaminopropyl acrylamide, di[2-(acryloyloxy)ethyl] phosphate, 2-acrylamido-2-methylpropanesulfonic acid and maleic acid. The method of grafting polar groups on the surface of cellulose is adopted, so that the content of free groups on the surface of cellulose is increased, and the newly introduced groups are polar groups, and the hydrophilicity is higher than that of hydroxyl groups, so that the liquid absorption capacity of the electrolytic capacitor paper is improved.

Description

Technical Field

[0001] This invention belongs to the field of special paper technology, and particularly relates to a method for preparing electrolytic capacitor paper. Background Technology

[0002] Aluminum electrolytic capacitors are key components of power supply systems for electronic devices, with extremely wide applications. In consumer electronics, they are widely used in televisions, computer power supplies, and other devices, primarily serving to stabilize voltage. In automotive electronics, they are compatible with key modules such as engine control systems and on-board chargers, ensuring reliable equipment operation. In industrial applications, they are essential components for inverters, UPS power supplies, and other equipment, undertaking core functions of filtering and energy storage. Electrolytic capacitor paper is one of the core components of electrolytic capacitors, primarily functioning to isolate the anode and cathode, prevent short circuits, and ensure smooth ion migration in the electrolyte. Liquid absorption is an important indicator of electrolytic capacitor performance. The electrolyte plays a crucial role in electrolytic capacitors, acting as both an ion conductor and a participant in electrode reactions. It provides ions for charge migration between the positive and negative electrodes, ensuring the electrochemical process during charging and discharging, while simultaneously wetting the electrolytic capacitor paper and electrodes, forming a stable conductive path. The electrolyte content in the electrolytic capacitor paper directly affects the capacitor's capacitance, leakage current, and lifespan.

[0003] The raw materials for electrolytic capacitor paper are usually plant fibers, such as wood pulp fiber, hemp pulp fiber, and cotton pulp fiber. These fibers possess a strong hydrophilicity due to their hydroxyl structure. However, to ensure the voltage withstand capability of electrolytic capacitors, the plant fibers used as raw materials typically need a high degree of beating to guarantee a high density in the electrolytic capacitor paper. However, the dense structure of the electrolytic capacitor paper reduces the content of free hydroxyl groups on the surface, leading to poor liquid absorption. Chinese patent application CN202510416878.1 proposes a method to improve the liquid absorption performance of electrolytic capacitor diaphragms. This method involves forming fibers into a long web, followed by heating and drying, and then freeze-drying under reduced pressure to increase the fine pore structure between the fibers, thereby improving the liquid absorption performance of the diaphragm. However, this method causes the free water in the cellulose to crystallize into ice crystals during the freeze-drying process. The formation of ice crystals can open up the gaps between fibers, leading to fiber breakage and dispersion, damaging the original interwoven structure, and easily causing problems such as fiber delamination and fuzzing in the paper, resulting in a decrease in paper strength. Summary of the Invention

[0004] In order to overcome the problems in the prior art, the present invention provides a method for preparing highly absorbent electrolytic capacitor paper, which solves the problem of poor absorbency caused by high density of electrolytic capacitor paper.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] This invention provides a method for preparing highly absorbent electrolytic capacitor paper, comprising the following steps; S1. Remove oxygen from the pulp after preparing it from the softwood pulp. S2. Add an initiator to the slurry in S1, stir evenly, then add a fiber modifying agent. After the reaction is complete, the modified slurry is obtained. The fiber modifying agent is selected from one or more of N,N-dimethylacrylamide, dimethylaminopropylacrylamide, di[2-(acryloyloxy)ethyl]phosphate, 2-acrylamido-2-methylpropanesulfonic acid, and maleic acid. S3. After thoroughly cleaning the slurry obtained in S2, wet papermaking is performed to obtain highly absorbent electrolytic capacitor paper.

[0007] To ensure the voltage resistance of electrolytic capacitor paper, the paper is generally highly compact and has a dense structure. This causes hydrogen bonds to form between the hydroxyl groups in the cellulose, reducing the number of free hydroxyl groups and thus decreasing the liquid absorption capacity of the capacitor paper. In this invention, graft modification of softwood pulp fibers adds new hydrophilic groups to the cellulose surface, increasing the number of hydrophilic groups. These introduced groups are charged and can generate strong electrostatic interactions with water molecules (polar molecules), exhibiting hydrophilicity far stronger than that of neutral hydroxyl groups. Specifically, an initiator is added to the softwood pulp fiber, which, through its own decomposition or reaction, generates active free radicals, cations, or anions, activating the active sites of the cellulose molecular chains. This improves the efficiency of the graft copolymerization reaction between cellulose molecules and the modifying agent, grafting amino, phosphate, or carboxylic acid groups onto the cellulose molecules.

[0008] As an optional implementation, in the preparation method provided by the present invention, the initiator is selected from one or more of sodium hydroxide, potassium persulfate, azobisisobutyramidine hydrochloride and triethanolamine.

[0009] As an optional implementation method, in the preparation method provided by the present invention, the dry weight of the softwood pulp to the mass ratio of the fiber modifying agent is 1:1 to 1:5.

[0010] As an optional implementation method, in the preparation method provided by the present invention, the amount of the initiator is 0.5 to 5% of the oven-dry weight of the softwood pulp.

[0011] In this invention, controlling the ratio of the oven-dry weight of the softwood pulp to the mass of the fiber-modifying agent and the initiator within the above-mentioned range is beneficial to ensuring the efficiency of the reaction and the cellulose grafting rate.

[0012] Furthermore, the preferred amount of initiator is 2 to 5% of the oven-dry weight of the softwood pulp.

[0013] As an optional implementation, in the preparation method provided by the present invention, in S1, the beating degree of the softwood pulp is 40-90°SR.

[0014] As an optional implementation, in the preparation method provided by the present invention, in S1, the heat preservation temperature of the softwood pulp is 40-80°C, and the oxygen in the pulp is removed by introducing nitrogen gas.

[0015] In this invention, appropriately increasing the reaction temperature will improve the reaction efficiency, but higher temperatures will accelerate the hydrolysis and breakage of glycosidic bonds in cellulose molecules, causing cellulose to turn yellow, weaken its mechanical strength, increase its brittleness, loosen its fiber structure, and reduce the number of surface active hydroxyl groups. Considering the long reaction time, the reaction temperature is controlled within 40 to 80°C.

[0016] As an optional implementation method, in the preparation method provided by the present invention, in step S2, after adding the fiber modifying agent, the mixture is stirred and reacted for 2 to 10 hours.

[0017] As an optional implementation, in the preparation method provided by the present invention, in step S3, the slurry is thoroughly washed with ethanol and deionized water in sequence.

[0018] As an optional implementation method, in the preparation method provided by the present invention, in S3, the wet papermaking adopts the forming method of a wire paper machine with a forming concentration of 0.1%, and after forming, it undergoes pressing, drying, curling, and slitting processes.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a method of grafting polar groups onto the surface of cellulose, thereby increasing the content of free groups on the cellulose surface. Moreover, the newly introduced groups are polar groups with higher hydrophilicity than hydroxyl groups, which improves the liquid absorption capacity of electrolytic capacitor paper without significantly altering the density and mechanical properties of the electrolytic capacitor paper. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with the specification and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] 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.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] Example 1 (1) Add softwood pulp (beating degree 80 °SR) to water, set the temperature to 60 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0024] (2) Add the initiator azobisisobutyramidine hydrochloride (3% of the mass of softwood pulp) to the pulp, stir for 10 min, then add the cellulose modifier N,N-dimethylacrylamide (the mass ratio of softwood pulp to N,N-dimethylacrylamide is 1:3), and continue stirring for 6 h.

[0025] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0026] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0027] Example 2 (1) Add softwood pulp (beating degree 80 °SR) to water, set the temperature to 60 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0028] (2) Add the initiator azobisisobutyramidine hydrochloride (3% of the mass of softwood pulp) to the pulp, stir for 10 min, then add the cellulose modifier N,N-dimethylacrylamide (the mass ratio of softwood pulp to N,N-dimethylacrylamide is 1:1), and continue stirring for 2 h.

[0029] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0030] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0031] Example 3 (1) Add softwood pulp (beating degree 80 °SR) to water, set the temperature to 60 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0032] (2) Add the initiator azobisisobutyramidine hydrochloride (5% of the mass of softwood pulp) to the pulp, stir for 10 min, then add the cellulose modifier N,N-dimethylacrylamide (the mass ratio of softwood pulp to N,N-dimethylacrylamide is 1:5), and continue stirring for 10 h.

[0033] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0034] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0035] Example 4 (1) Add softwood pulp (beating degree 90 °SR) to water, set the temperature to 80 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0036] (2) Add the initiator triethanolamine (2% of the mass of softwood pulp) to the pulp, stir for 5 min, then add the cellulose modifier di[2-(acryloyloxy)ethyl] phosphate (the mass ratio of softwood pulp to di[2-(acryloyloxy)ethyl] phosphate is 1:2), and then continue stirring for 6 h.

[0037] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0038] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0039] Example 5 (1) Add softwood pulp (beating degree 40 °SR) to water, set the temperature to 40 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0040] (2) Add potassium persulfate (2% of the weight of softwood pulp) to the pulp as an initiator, stir for 5 min and then add 2-acrylamide-2-methylpropanesulfonic acid (the mass ratio of softwood pulp to 2-acrylamide-2-methylpropanesulfonic acid is 1:2), and then continue stirring for 6 h.

[0041] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0042] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0043] Comparative Example 1 (1) Add softwood pulp (beating degree 80 °SR) to water, set the temperature to 60 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0044] (2) The softwood pulp is wet-processed (formed by a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled and cut to obtain electrolytic capacitor paper.

[0045] Comparative Example 2 (1) Add softwood pulp (beating degree 80 °SR) to water, set the temperature to 60 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0046] (2) Add the initiator azobisisobutyramidine hydrochloride (3% of the weight of softwood pulp) to the pulp, stir for 10 min to disperse evenly, and continue stirring for 6 h.

[0047] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0048] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0049] Comparative Example 3 (1) Add softwood pulp (beating degree 80 °SR) to water, set the temperature to 60 °C and stir evenly. Then, pass nitrogen into the pulp to remove oxygen from the pulp.

[0050] (2) Add cellulose-modifying agent N,N-dimethylacrylamide (the mass ratio of softwood pulp to N,N-dimethylacrylamide is 1:3) to the pulp, stir evenly and continue stirring for 6 h.

[0051] (3) After the reaction is complete, wash the slurry thoroughly with ethanol and deionized water in sequence to remove the reagents.

[0052] (4) Clean softwood pulp is wet-processed (formed on a wire paper machine with a forming concentration of 0.1%, and after forming, it is pressed, dried, rolled, and slit to obtain electrolytic capacitor paper.

[0053] Performance testing The thickness of the electrolytic capacitor paper was tested according to GB / T 451.3-2023 "Determination of Thickness of Paper and Paperboard", the tensile strength was tested according to GB / T 12914-2023 "Determination of Tensile Strength of Paper and Paperboard", and the liquid absorption height was tested according to GB / T 461.1-2002 "Determination of Capillary Height of Paper and Paperboard (Klem Method)". The test results of each group of electrolytic capacitor paper samples are shown in the table below: Table 1: Performance Test Results of Electrolytic Capacitor Paper

[0054] As shown in Table 1, compared with Comparative Example 1, Examples 1-5 all showed a significant increase in liquid absorption height, while the density and tensile strength remained largely unchanged. The liquid absorption height of Comparative Example 2 decreased significantly, possibly because the initiator activated the hydroxyl groups on the cellulose surface, making them more prone to forming hydrogen bonds during molding, thus reducing the number of free hydrogen bonds. The liquid absorption of Comparative Example 3 decreased somewhat, likely due to the lack of an initiator to enhance hydroxyl activity, making it more difficult for the cellulose modifying agent to react with the cellulose. As shown in Table 1, comparing Examples 1-3, it can be seen that with increasing amounts of cellulose modifying agent and reaction time, the liquid absorption height of the electrolytic capacitor paper initially increased significantly and then stabilized at a relatively stable level.

[0055] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing highly absorbent electrolytic capacitor paper, characterized in that, Includes the following steps; S1. Remove oxygen from the pulp after preparing it from the softwood pulp. S2. Add an initiator to the slurry in S1, stir evenly, then add a fiber modifying agent. After the reaction is complete, the modified slurry is obtained. The fiber modifying agent is selected from one or more of N,N-dimethylacrylamide, dimethylaminopropylacrylamide, di[2-(acryloyloxy)ethyl]phosphate, 2-acrylamido-2-methylpropanesulfonic acid, and maleic acid. S3. After thoroughly cleaning the slurry obtained in S2, wet papermaking is performed to obtain highly absorbent electrolytic capacitor paper.

2. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, The initiator is selected from one or more of sodium hydroxide, potassium persulfate, azobisisobutyramidine hydrochloride, and triethanolamine.

3. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, The oven-dry weight of the softwood pulp to the mass ratio of the fiber modifying agent is 1:1 to 1:

5.

4. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, The oven-dry weight of the softwood pulp to the mass ratio of the fiber modifying agent is 1:2 to 1:

5.

5. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, The amount of the initiator is 0.5 to 5% of the oven-dry weight of the softwood pulp.

6. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, In S1, the beating degree of the softwood pulp is 40-90°SR.

7. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, In S1, the insulation temperature of softwood pulp is 40-80℃, and nitrogen gas is introduced to remove oxygen from the pulp.

8. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, In S2, after adding fiber-modifying reagent, the mixture is stirred and reacted for 2–10 h.

9. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, In S3, the slurry is thoroughly cleaned with ethanol and deionized water in sequence.

10. The method for preparing highly absorbent electrolytic capacitor paper according to claim 1, characterized in that, In S3, wet papermaking uses a wire paper machine forming method with a forming concentration of 0.1%. After forming, the paper undergoes pressing, drying, curling, and slitting.

Images