A leak-proof paste layer paper, its preparation method and application in carbon batteries

Abstract

This invention relates to the field of battery materials technology, specifically to a leak-proof pulp layer paper, its preparation method, and its application in carbon-zinc batteries. The leak-proof pulp layer paper comprises, from the outside to the inside, an anti-corrosion coating, a dense core layer, and a seepage-proof surface layer, constructing multiple liquid-resistant and anti-corrosion barriers. The dense core layer comprises the following components by weight: softwood pulp, polypropylene fiber, modified starch, vinyl dimethyl fluorosilane-modified nano-silicon nitride, fumed silica, mixed monomers, initiator, and crosslinking agent. Softwood pulp provides basic strength, polypropylene fiber enhances electrolyte resistance, modified starch improves adhesion and retention, and the mixed monomers and modified nano-silicon nitride form a three-dimensional crosslinked structure. This results in high tensile strength, no swelling upon immersion, no deformation, and no collapse, significantly improving the interfacial bonding strength, leak-proof performance, and structural stability of the pulp layer paper, achieving multiple effects of efficient leak prevention, corrosion prevention, and stable discharge.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a leak-proof pulp layer paper, its preparation method, and its application in carbon batteries. Background Technology

[0002] Carbon-zinc batteries, also known as neutral zinc-manganese dioxide dry cell batteries, can be structurally classified into paste-type batteries and cardboard batteries. Batteries using a paper pulp layer as a separator are called cardboard batteries. Due to their low cost and reliable operation, carbon-zinc batteries are widely used in various small electronic and electrical products.

[0003] The electrolyte in a carbon-zinc battery is primarily an aqueous solution of zinc chloride and ammonium chloride. The positive electrode consists of electrolytic manganese dioxide, acetylene black, and graphite, with a conductive carbon rod inserted at the center as a current collector. Zinc metal, due to its low hydrogen evolution overpotential, also serves as the negative electrode and is integrated into the battery casing. A paper separator physically isolates the positive and negative electrodes to prevent internal short circuits while ensuring the smooth passage of conductive ions in the electrolyte, thus maintaining normal battery discharge.

[0004] However, during actual use, long-term storage, or intermittent discharge, the negative electrode of the zinc cylinder is prone to contact corrosion with the acidic electrolyte, leading to continuous consumption of the zinc layer and a decrease in battery capacity. At the same time, the pulp paper is prone to swelling, damage, and structural failure in the electrolyte, which further aggravates the corrosion rate of the zinc cylinder, eventually causing perforation of the zinc cylinder and leakage of electrolyte, which in turn corrodes the electrical equipment, resulting in safety hazards and economic losses.

[0005] To reduce the risk of leakage, existing carbon-zinc batteries have to use thicker zinc canisters to ensure structural strength and corrosion resistance. This results in a large amount of zinc canister material and weight, significantly increasing battery production costs and limiting the improvement of product cost-effectiveness. Therefore, optimizing the structure and materials of the pulp paper adhering to the inner wall of the zinc canister, based on the corrosion and leakage mechanisms during battery storage and discharge, to improve the corrosion resistance, liquid barrier, and swelling resistance of the pulp paper without reducing battery discharge performance, thereby reducing the zinc canister wall thickness, reducing zinc canister material usage, and lowering production costs, has become a key technical problem that urgently needs to be solved in the field of carbon-zinc batteries. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a leak-proof pulp layer paper and its preparation method for use in carbon batteries.

[0007] The objective of this invention is achieved through the following technical solution: a leak-proof pulp layer paper, comprising an anti-corrosion coating, a dense core layer, and an impermeable surface layer arranged sequentially from the outside to the inside, wherein the dense core layer comprises the following components by weight: 75-85 parts softwood pulp, 10-15 parts polypropylene fiber, 4-6 parts modified starch, 2-4 parts vinyl dimethyl fluorosilane modified nano-silicon nitride, 1-3 parts fumed silica, 4-9 parts mixed monomers, 0.5-1 parts initiator, and 0.1-0.3 parts crosslinking agent.

[0008] This invention utilizes a three-layer gradient structure consisting of an anti-corrosion coating, a dense core layer, and a seepage-proof surface layer. The anti-corrosion coating inhibits corrosion, the dense core layer blocks liquid, and the seepage-proof surface layer prevents seepage, thus constructing a multi-layered liquid-blocking and anti-corrosion barrier. The dense core layer, serving as the core support and key layer for liquid blocking in this three-layer structure, is primarily composed of softwood pulp fibers. These fibers are of moderate length and uniformly dispersed, ensuring the paper's paper-forming properties, surface smoothness, and basic mechanical strength. Polypropylene fibers are synergistically blended with softwood pulp. Due to their excellent acid resistance, electrolyte resistance, and non-swelling and non-deformation properties, these fibers significantly improve the wet strength and dimensional stability of the dense core layer, preventing softening, damage, and bulging of the core layer under long-term immersion in electrolytes. The problem is to ensure a tight bond with the positive electrode carbon powder; modified starch, as an auxiliary binder and retention aid, can effectively improve the bonding force between softwood pulp and polypropylene fiber, enhance the retention rate of functional fillers such as vinyl dimethyl fluorosilane modified nano silicon nitride and fumed silica, while significantly reducing the hydrophilicity of the core layer, improving the resistance to electrolyte swelling, and without affecting the battery's ion conduction and overall leak-proof effect. It also has good compatibility with the anti-seepage surface layer and anti-corrosion coating, avoiding defects such as poor compatibility and delamination between layers. Vinyl dimethyl fluorosilane-modified nano-silicon nitride and fumed silica work synergistically in the dense core layer to construct a dense physical liquid barrier. This effectively fills fiber gaps, reduces core layer pore size, and prevents electrolyte penetration along capillary pores, while not blocking ion transport channels, ensuring that battery discharge performance does not decline. The vinyl dimethyl fluorosilane-modified nano-silicon nitride undergoes surface modification treatment, with vinyl and fluoromethyl groups grafted onto its surface. This not only provides good dispersibility, preventing filler agglomeration and leakage weaknesses, but also excellent liquid repellency, resistance to electrolyte corrosion, and copolymerization reactivity. It can undergo cross-linking reactions with the mixed monomers to form a stable three-dimensional cross-linked network, significantly improving the structural stability and interfacial bonding strength of the dense core layer. The mixed monomers, as the core functional components of the dense core layer, work synergistically with the other raw materials to further enhance core layer performance and interfacial bonding effects.

[0009] Furthermore, the anti-corrosion coating is a water-based phosphate ester anti-corrosion coating. The phosphate ester reacts with zinc to form a dense passivation film, preventing zinc from being corroded by the electrolyte. The anti-seepage surface layer is a PVDF anti-seepage coating, which blocks the electrolyte from flowing randomly to the positive electrode side, preventing electrolyte loss and short circuits.

[0010] Furthermore, the mixed monomers include 8-12 parts of styrene, 7-10 parts of dodecafluoroheptyl methacrylate, 6-9 parts of phosphate acrylate monomers, and 2-6 parts of acrylate-terminated organosilicon monomers.

[0011] In this invention, the mixed monomers are complementary and synergistic. Styrene improves the mechanical properties of the dense core layer. Dodecafluoroheptyl methacrylate contains a long-chain fluoroalkyl group, which can form strong fluorine-fluorine intermolecular forces with the fluorine structure of the PVDF waterproofing surface layer, strengthening the interfacial bonding between the core layer and the waterproofing surface layer and preventing coating peeling. Phosphate acrylate monomers can form hydrogen bonds with the modified silicon nitride and fibers in the dense core layer, while also helping to improve the corrosion resistance of the core layer and balance interfacial polarity. More importantly, the phosphate groups in the phosphate acrylate monomer molecules can... The phosphate ester components in the phosphate ester waterborne anti-corrosion coating exhibit strong molecular interactions, while their acrylate end groups can tightly bind to the core layer cross-linking network. This significantly improves the connection performance between the dense core layer and the anti-corrosion coating, enhances interlayer adhesion, and prevents the anti-corrosion coating from peeling off from the core layer. The acrylate-terminated organosilicon monomers synergistically enhance the core layer's electrolyte resistance and high / low temperature resistance with the silicon-fluorine structure of vinyldimethylfluorosilane-modified nano-silicon nitride. Simultaneously, they cross-link with other monomers to form a flexible network, adapting to battery assembly deformation, preventing core layer cracking, and without affecting ion conduction. Furthermore, the mixed monomers can undergo copolymerization with modified silicon nitride to construct a stable three-dimensional cross-linking network, further improving the structural stability, density, and mechanical strength of the dense core layer, providing strong support for multiple protections including corrosion inhibition, liquid barrier, and seepage prevention.

[0012] Furthermore, the initiator is ammonium persulfate, and the crosslinking agent is N,N'-methylenebisacrylamide.

[0013] Furthermore, the preparation method of the vinyldimethylfluorosilane modified nano-silicon nitride includes the following steps: A1. Add nano-silicon nitride particles to anhydrous ethanol and ultrasonically disperse for 40-60 min to obtain nano-silicon nitride suspension; A2. Dissolve vinyldimethylfluorosilane in anhydrous ethanol, then slowly add deionized water to obtain a vinyldimethylfluorosilane hydrolysate. A3. Under nitrogen protection, the vinyl dimethyl fluorosilane hydrolysate is added dropwise to the nano silicon nitride suspension, and the mixture is magnetically stirred until homogeneous. The reaction is carried out at 50-70℃ for 2-3 hours. A4. After the reaction is complete, the solvent is removed by rotary evaporation to obtain vinyl dimethyl fluorosilane modified nano silicon nitride.

[0014] In this invention, the siloxane group of vinyl dimethyl fluorosilane undergoes a condensation reaction with the hydroxyl groups on the surface of nano-silicon nitride to achieve covalent coating; the vinyl group at the end of the molecular chain can participate in subsequent free radical grafting polymerization, and the fluoromethyl group imparts low surface energy and hydrophobicity to the surface, achieving strong interfacial bonding between inorganic fillers and organic systems.

[0015] Furthermore, the amount of vinyldimethylfluorosilane added is 3-15% of the mass of nano-silicon nitride.

[0016] Furthermore, the particle size of the nano-silicon nitride is 20-80 nm; the particle size of the fumed silica is 10-40 nm.

[0017] Furthermore, the thickness of the anti-corrosion coating is 0.3-0.5 μm; the thickness of the dense core layer is 80-100 μm; and the thickness of the impermeable surface layer is 0.5-1 μm.

[0018] Furthermore, the preparation method of the modified starch includes the following steps: B1. Mix starch and water in a mass ratio of 1:3-5 until they are completely dispersed and free of granules. Then, heat the mixture to 85-95℃ and stir at low speed for 30-40 minutes to obtain gelatinized starch. B2. Lower the system temperature to 70-75℃ and adjust the pH to 6-7. Then add α-amylase and perform the first enzymatic hydrolysis reaction for 60-90 minutes to obtain short-chain starch. B3. Lower the system temperature to 55-60℃ and adjust the pH to 4.5-5.5. Then add glucoamylase and perform a second enzymatic hydrolysis reaction for 90-120 min to obtain refined starch. B4. Lower the system temperature to 45-55℃ and adjust the pH to 6.5-7.5. Then add the compound enzyme and perform the third enzymatic hydrolysis reaction for 120-180 min. Next, raise the temperature to 95-100℃ for inactivation treatment for 10-15 min. Centrifuge, dehydrate, wash, dry and pulverize to obtain modified starch of 100-200 mesh.

[0019] Furthermore, the amount of α-amylase added is 0.1-0.3% of the starch mass; the amount of glucoamylase added is 0.2-0.5% of the starch mass; and the amount of the complex enzyme added is 0.1-0.2% of the starch mass.

[0020] Furthermore, the complex enzyme is a decarboxylase and an oxidative dehydrogenase, wherein the decarboxylase and the oxidative dehydrogenase are mixed in a mass ratio of 1:1.8-2.2.

[0021] The modified starch of this invention is first enzymatically hydrolyzed stepwise by α-amylase and glucoamylase to reduce molecular weight and viscosity; then, it is modified by decarboxylase and dehydrogenase to remove hydroxyl and carboxyl groups, reduce the number of hydrophilic groups, and improve hydrophobicity and resistance to electrolyte corrosion, ultimately obtaining low polarity enzymatically hydrolyzed starch suitable for battery pulp paper.

[0022] Furthermore, the method for preparing the dense core layer includes the following steps: C1. Mix softwood pulp and polypropylene fiber according to the specified ratio, put them into a high-consistency pulper, adjust the fiber length to 0.8-1.2mm, add deionized water, and prepare a mixed fiber pulp with a fiber mass concentration of 18-22% for later use. C2. Mix the modified starch and water at a mass ratio of 1:3-5, heat to 85-90℃ and keep warm for 30 minutes to fully gelatinize until there are no particles and the mixture is fluid and uniform. Cool down to 55-60℃ and set aside. C3. Mix the mixed fiber slurry from step C1, vinyl dimethyl fluorosilane modified nano-silicon nitride, fumed silica, and gelatinized modified starch from step C2. After stirring evenly, heat to 65-70℃, add the mixed monomers, initiator, and crosslinking agent in sequence, and continue stirring at a low speed of 300-400 rpm / min for 30-45 min. After the reaction is complete, adjust the solid content of the slurry to 25%-30% to obtain a dense core layer molding slurry. C4. Feed the dense core layer forming slurry from step C3 into the inclined wire paper machine, control the paper machine speed to 15-20m / min, and pass through the forming, pressing and pre-drying processes in sequence to obtain the dense core layer.

[0023] Further, in step C4, the forming step involves evenly spreading the dense core layer forming slurry on the wire screen, removing excess water, and initially forming a wet paper web; the pressing step involves using a two-roll press at a pressure of 1.2-1.5 MPa to remove free water from the wet paper web, and controlling the moisture content of the paper web to 45%-50% after pressing; the pre-drying step involves segmented hot air drying, with the temperature in zone one at 75-80℃ and the temperature in zone two at 85-90℃, reducing the moisture content of the paper web to 8-10% after drying, obtaining a dense core layer base paper with a basis weight controlled at 28-32 g / m². 2 Thickness 80-100μm, porosity 20-25%.

[0024] The present invention also provides a method for preparing the aforementioned leak-proof pulp layer paper, comprising the following steps: S1. Fix the dense core paper and apply a water-based anti-corrosion emulsion of phosphate ester to its outer side using a micro-gravure coating method at a coating speed of 20-25 m / min. After coating, put it into an oven and dry at 65-70℃ for 10-15 min to form an anti-corrosion coating on the outer side of the dense core paper. S2. Turn the base paper with the anti-corrosion coating over and apply PVDF aqueous dispersion to the inner side of the core layer using a doctor blade coating method at a coating speed of 18-22 m / min. After coating, dry at 70-75℃ for 15-20 min to solidify and form an impermeable surface layer on the inner side of the dense core layer base paper, thus obtaining the leak-proof pulp layer paper.

[0025] The preparation method of this invention is simple to operate and easy to control, which is conducive to large-scale industrial production. The resulting high water-resistant, leak-proof polyethylene paper has stable quality and can be widely used in carbon-zinc batteries.

[0026] This invention also provides an application of the above-mentioned leak-proof slurry layer paper in a carbon-zinc battery, wherein the anti-corrosion coating is used to adhere to one side of the zinc canister, and the impermeable surface layer is used to contact the positive electrode carbon powder. The anti-corrosion coating focuses on corrosion inhibition and protection on the zinc canister side, the dense core layer focuses on dense liquid barrier and structural support, and the impermeable surface layer focuses on liquid-repellent and impermeable protection on the positive electrode carbon powder side.

[0027] The beneficial effects of this invention are as follows: (1) This invention achieves integrated protection of corrosion inhibition, liquid blocking, seepage prevention and solidification through a three-layer gradient structure of anti-corrosion coating, dense core layer and seepage-proof surface layer. The anti-corrosion coating forms a dense passivation film on the zinc cylinder surface to inhibit electrochemical corrosion. The dense core layer fills the pores with nano-silicon nitride and fumed silica to build a physical liquid barrier. The seepage-proof surface layer uses PVDF to achieve hydrophobic seepage prevention. The three together block the electrolyte penetration path and prevent leakage during long-term storage.

[0028] (2) The phosphate esters and acrylates in the mixed monomers significantly improve the adhesion between the core layer and the phosphate ester anti-corrosion coating; dodecafluoroheptyl methacrylate forms fluorine with PVDF. The strong effect of fluorine ensures a tight bond between the impermeable surface layer and the core layer; combined with the cross-linking network, the adhesion of both the anti-corrosion layer and the impermeable layer reaches level 0, preventing peeling and curling even after long-term immersion.

[0029] (3) Softwood pulp provides basic strength, polypropylene fiber improves resistance to electrolyte, modified starch improves adhesion and retention, and mixed monomers and modified nano-silicon nitride form a three-dimensional cross-linked structure, resulting in high tensile strength, no swelling after immersion, no deformation, and no collapse.

[0030] (4) The core layer has moderate porosity, and the nanofillers and functional monomers do not block the ion channels. The high ion conductivity ensures stable battery discharge and no capacity decay, achieving anti-seepage and non-blocking properties. (5) The preparation process is simple and the parameters are controllable. The finished product has uniform thickness and smooth surface. It can be applied to carbon zinc manganese batteries, which can reduce the thickness of zinc cylinder wall and reduce battery cost. It has significant economic and application value. Detailed Implementation

[0031] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0032] Example 1 This embodiment provides a leak-proof pulp layer paper, comprising, from the outside to the inside, an anti-corrosion coating, a dense core layer, and a seepage-proof surface layer, wherein the dense core layer comprises the following components by weight: 75 parts softwood pulp, 10 parts polypropylene fiber, 4 parts modified starch, 2 parts vinyl dimethyl fluorosilane modified nano-silicon nitride, 1 part fumed silica, 4 parts mixed monomers, 0.5 parts initiator, and 0.1 parts crosslinking agent.

[0033] Furthermore, the anti-corrosion coating is a phosphate ester water-based anti-corrosion coating; the anti-seepage surface layer is a PVDF anti-seepage coating.

[0034] Furthermore, the mixed monomers include 10 parts styrene, 8 parts dodecafluoroheptyl methacrylate, 8 parts phosphate acrylate monomers, and 4 parts acrylate-terminated organosilicon monomers.

[0035] In this embodiment, the acrylate-terminated organosilicon monomer has a relative molecular mass of 6000 and is selected from Guangzhou Sloco Polymer Co., Ltd., with model number 3821F42. The phosphate acrylate monomer is selected as 2-hydroxyethyl methacrylate phosphate.

[0036] Furthermore, the initiator is ammonium persulfate, and the crosslinking agent is N,N'-methylenebisacrylamide.

[0037] Furthermore, the preparation method of the vinyldimethylfluorosilane modified nano-silicon nitride includes the following steps: A1. Add nano-silicon nitride particles to anhydrous ethanol and ultrasonically disperse for 50 min to obtain nano-silicon nitride suspension; A2. Dissolve vinyldimethylfluorosilane in anhydrous ethanol, then slowly add deionized water to obtain a vinyldimethylfluorosilane hydrolysate. A3. Under nitrogen protection, the vinyl dimethyl fluorosilane hydrolysate was added dropwise to the nano silicon nitride suspension, and the mixture was magnetically stirred until homogeneous. The reaction was carried out at 60°C for 2 hours. A4. After the reaction is complete, the solvent is removed by rotary evaporation to obtain vinyl dimethyl fluorosilane modified nano silicon nitride.

[0038] Furthermore, the amount of vinyldimethylfluorosilane added is 12% of the mass of nano-silicon nitride.

[0039] Furthermore, the particle size of the nano-silicon nitride is 60 nm; the particle size of the fumed silica is 30 nm.

[0040] Furthermore, the thickness of the anti-corrosion coating is 0.4 μm; the thickness of the dense core layer is 90 μm; and the thickness of the impermeable surface layer is 0.8 μm.

[0041] Furthermore, the preparation method of the modified starch includes the following steps: B1. Mix starch and water in a mass ratio of 1:4 until they are completely dispersed and free of granules. Then, heat the mixture to 90°C and stir at low speed for 35 minutes to obtain gelatinized starch. B2. Lower the system temperature to 73℃ and adjust the pH to 6-7. Then add α-amylase and perform the first enzymatic hydrolysis reaction for 80 minutes to obtain short-chain starch. B3. Lower the system temperature to 58℃ and adjust the pH to 4.5-5.5. Then add glucoamylase and perform a second enzymatic hydrolysis reaction for 100 minutes to obtain refined starch. B4. Lower the system temperature to 50℃ and adjust the pH to 6.5-7.5. Then add the compound enzyme and perform a third enzymatic hydrolysis reaction for 150 min. Next, raise the temperature to 100℃ for inactivation treatment for 12 min. Centrifuge, dehydrate, wash, dry and pulverize to obtain 150 mesh modified starch.

[0042] Furthermore, the amount of α-amylase added is 0.2% of the starch mass; the amount of glucoamylase added is 0.3% of the starch mass; and the amount of the complex enzyme added is 0.2% of the starch mass.

[0043] Furthermore, the complex enzyme is a decarboxylase and an oxidative dehydrogenase, wherein the decarboxylase and the oxidative dehydrogenase are mixed in a mass ratio of 1:2.

[0044] Furthermore, the method for preparing the dense core layer includes the following steps: C1. Mix softwood pulp and polypropylene fiber according to the specified ratio, put them into a high-consistency pulper, adjust the fiber length to 1mm, add deionized water, and prepare a mixed fiber pulp with a fiber mass concentration of 20% for later use. C2. Mix the modified starch and water at a mass ratio of 1:4, heat to 88℃ and keep warm for 30 minutes until fully gelatinized until there are no particles and the mixture is fluid and uniform. Then cool to 58℃ and set aside. C3. Mix the mixed fiber slurry from step C1, vinyl dimethyl fluorosilane modified nano-silicon nitride, fumed silica and gelatinized modified starch from step C2, stir evenly and heat to 68°C, add mixed monomers, initiator and crosslinking agent in sequence, and continue to stir at a low speed of 350 rpm / min for 40 min. After the reaction is completed, adjust the solid content of the slurry to 28% to obtain a dense core layer molding slurry. C4. The dense core layer forming slurry from step C3 is fed into an inclined wire paper machine, and the paper machine speed is controlled at 18m / min. The slurry passes through forming, pressing, and pre-drying processes in sequence to obtain a dense core layer.

[0045] Further, in step C4, the forming step involves evenly spreading the dense core layer forming slurry on the wire screen, removing excess water, and initially forming a wet paper web; the pressing step involves using a two-roll press at a pressure of 1.3 MPa to remove free water from the wet paper web, and controlling the moisture content of the paper web at 48% after pressing; the pre-drying step involves segmented hot air drying, with a temperature of 78°C in zone one and 88°C in zone two, reducing the moisture content of the paper web to 9% after drying, obtaining a dense core layer base paper with a basis weight controlled at 30 g / m². 2 Thickness 90μm, porosity 25%.

[0046] This embodiment also provides a method for preparing the aforementioned leak-proof pulp layer paper, comprising the following steps: S1. Fix the dense core paper and apply a phosphate ester water-based anti-corrosion emulsion to its outer side using a micro-gravure coating method at a coating speed of 23 m / min. After coating, send it into an oven and dry at 68°C for 12 min to cure and form an anti-corrosion coating on the outer side of the dense core paper. S2. Turn the base paper with the anti-corrosion coating over and apply PVDF aqueous dispersion to the inner side of the core layer using a doctor blade coating method at a coating speed of 20 m / min. After coating, dry at 73°C for 18 min to solidify and form an impermeable surface layer on the inner side of the dense core layer base paper, thus obtaining the leak-proof pulp layer paper.

[0047] This embodiment also provides an application of the above-mentioned leak-proof slurry layer paper in a carbon-zinc battery. The anti-corrosion coating is used to adhere to one side of the zinc cylinder, and the impermeable surface layer is used to contact the positive electrode carbon powder. The anti-corrosion coating focuses on corrosion inhibition and protection on the zinc cylinder side, the dense core layer focuses on dense liquid barrier and structural support, and the impermeable surface layer focuses on liquid-repellent and impermeable protection on the positive electrode carbon powder side.

[0048] Example 2 Unlike Example 1, the dense core layer of this example comprises the following components by weight: 80 parts softwood pulp, 12 parts polypropylene fiber, 5 parts modified starch, 3 parts vinyl dimethyl fluorosilane modified nano silicon nitride, 2 parts fumed silica, 7 parts mixed monomers, 0.8 parts initiator and 0.2 parts crosslinking agent.

[0049] Furthermore, the method for preparing the dense core layer includes the following steps: C1. Mix softwood pulp and polypropylene fiber according to the specified ratio, put them into a high-consistency pulper, adjust the fiber length to 1mm, add deionized water, and prepare a mixed fiber pulp with a fiber mass concentration of 20% for later use. C2. Mix the modified starch and water at a mass ratio of 1:4, heat to 88℃ and keep warm for 30 minutes until fully gelatinized until there are no particles and the mixture is fluid and uniform. Then cool to 58℃ and set aside. C3. Mix the mixed fiber slurry from step C1, vinyl dimethyl fluorosilane modified nano-silicon nitride, fumed silica and gelatinized modified starch from step C2, stir evenly and heat to 68°C, add mixed monomers, initiator and crosslinking agent in sequence, and continue to stir at a low speed of 350 rpm / min for 40 min. After the reaction is completed, adjust the solid content of the slurry to 28% to obtain a dense core layer molding slurry. C4. The dense core layer forming slurry from step C3 is fed into an inclined wire paper machine, and the paper machine speed is controlled at 18m / min. The slurry passes through forming, pressing, and pre-drying processes in sequence to obtain a dense core layer.

[0050] Further, in step C4, the forming step involves evenly spreading the dense core layer forming slurry on the wire screen, removing excess water, and initially forming a wet paper web; the pressing step involves using a two-roll press at a pressure of 1.4 MPa to remove free water from the wet paper web, and controlling the moisture content of the paper web at 48% after pressing; the pre-drying step involves segmented hot air drying, with a temperature of 78°C in zone one and 88°C in zone two, reducing the moisture content of the paper web to 9% after drying, obtaining a dense core layer base paper with a basis weight controlled at 30 g / m². 2 Thickness 90μm, porosity 23%.

[0051] Example 3 Unlike Example 1, the dense core layer described in this example comprises the following components by weight: 85 parts softwood pulp, 15 parts polypropylene fiber, 6 parts modified starch, 4 parts vinyl dimethyl fluorosilane modified nano-silicon nitride, 3 parts fumed silica, 9 parts mixed monomers, 1 part initiator, and 0.3 parts crosslinking agent.

[0052] Furthermore, the method for preparing the dense core layer includes the following steps: C1. Mix softwood pulp and polypropylene fiber according to the specified ratio, put them into a high-consistency pulper, adjust the fiber length to 1mm, add deionized water, and prepare a mixed fiber pulp with a fiber mass concentration of 20% for later use. C2. Mix the modified starch and water at a mass ratio of 1:4, heat to 88℃ and keep warm for 30 minutes until fully gelatinized until there are no particles and the mixture is fluid and uniform. Then cool to 58℃ and set aside. C3. Mix the mixed fiber slurry from step C1, vinyl dimethyl fluorosilane modified nano-silicon nitride, fumed silica and gelatinized modified starch from step C2, stir evenly and heat to 68°C, add mixed monomers, initiator and crosslinking agent in sequence, and continue to stir at a low speed of 350 rpm / min for 40 min. After the reaction is completed, adjust the solid content of the slurry to 28% to obtain a dense core layer molding slurry. C4. The dense core layer forming slurry from step C3 is fed into an inclined wire paper machine, and the paper machine speed is controlled at 18m / min. The slurry passes through forming, pressing, and pre-drying processes in sequence to obtain a dense core layer.

[0053] Further, in step C4, the forming step involves evenly spreading the dense core layer forming slurry on the wire screen, removing excess water, and initially forming a wet paper web; the pressing step involves using a two-roll press at a pressure of 1.5 MPa to remove free water from the wet paper web, and controlling the moisture content of the paper web at 48% after pressing; the pre-drying step involves segmented hot air drying, with a temperature of 78°C in zone one and 88°C in zone two, reducing the moisture content of the paper web to 9% after drying, obtaining a dense core layer base paper with a basis weight controlled at 30 g / m². 2 Thickness 90μm, porosity 20%.

[0054] Comparative Example 1 Unlike Example 2, an equal amount of starch was used to replace the modified starch in Example 2; that is, the modified starch in Example 2 was not modified. The resulting dense core paper had a porosity of 28%.

[0055] Comparative Example 2 Unlike Example 2, an equal amount of nano-silicon nitride was used to replace the vinyldimethylfluorosilane-modified nano-silicon nitride in Example 2; that is, the vinyldimethylfluorosilane-modified nano-silicon nitride in Example 2 was not modified. The porosity of the resulting dense core paper was 27%.

[0056] Comparative Example 3 Unlike Example 2, an equal amount of styrene was used to replace dodecafluoroheptyl methacrylate. This resulted in a dense core paper with a porosity of 25%.

[0057] Comparative Example 4 Unlike Example 2, an equal amount of styrene was used to replace the acrylate-terminated silicone monomers. This resulted in a dense core paper with a porosity of 24%.

[0058] Comparative Example 5 Unlike Example 2, the dense core layer of Example 2 was replaced with mercury-free pulp paper (ordinary type) produced by Guangdong Zhaoqing Mingzhu Paper Industry Co., Ltd., and its porosity was similar to that of the dense core layer of Example 2.

[0059] Performance testing This invention conducts performance tests on the anti-leakage pulp layer paper prepared in Example 2 and Comparative Examples 1-4, including tests on ionic conductivity, leakage resistance, tensile strength, and adhesion of the anti-corrosion coating and the anti-seepage surface layer. The test results are shown in Table 1 below: Table 1

[0060] The method for testing ionic conductivity is as follows: The ionic conductivity of the examples and comparative examples is tested using the AC impedance method. The pulp paper is cut into circular samples with a diameter of 18 mm. Stainless steel is used to replace the positive and negative electrode plates and assembled into a blocking battery (stainless steel sheet / pulp paper / stainless steel sheet). The bulk impedance at 40°C is tested using an electrochemical workstation. The ionic conductivity is calculated according to the formula: Ionic conductivity = pulp paper thickness / (bulk resistance × effective contact area) ×.

[0061] Test method for leakage resistance: Using the examples and comparative examples as the pulp paper for carbon batteries, zinc-manganese batteries were assembled according to GB8897-2008-T, and the leakage resistance of the batteries was tested.

[0062] Tensile strength test method: The examples and comparative examples were cut into dumbbell-shaped specimens with a length of 6 mm and a width of 4 mm. The specimens were stretched using an electronic universal testing machine at 30°C and a tensile rate of 5 mm / min to test the tensile strength.

[0063] Adhesion test method: The cross-cut test is conducted according to GB / T 9286–1998 "Cross-cut test of paint and varnish film".

[0064] The specific embodiments described above are further illustrations of the technical solution and beneficial effects of the present invention, and are not intended to limit the implementation methods. For those skilled in the art, any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A leak-proof pulp layer paper, characterized in that: It includes an anti-corrosion coating, a dense core layer, and a waterproof surface layer arranged sequentially from the outside to the inside. The dense core layer comprises the following components by weight: 75-85 parts softwood pulp, 10-15 parts polypropylene fiber, 4-6 parts modified starch, 2-4 parts vinyl dimethyl fluorosilane modified nano-silicon nitride, 1-3 parts fumed silica, 4-9 parts mixed monomers, 0.5-1 parts initiator, and 0.1-0.3 parts crosslinking agent.

2. The anti-leakage pulp layer paper according to claim 1, characterized in that: The mixed monomers include 8-12 parts of styrene, 7-10 parts of dodecafluoroheptyl methacrylate, 6-9 parts of phosphate acrylate monomers, and 2-6 parts of acrylate-terminated organosilicon monomers.

3. The anti-leakage pulp layer paper according to claim 1, characterized in that: The preparation method of the vinyl dimethyl fluorosilane modified nano silicon nitride includes the following steps: A1. Add nano-silicon nitride particles to anhydrous ethanol and ultrasonically disperse for 40-60 min to obtain nano-silicon nitride suspension; A2. Dissolve vinyldimethylfluorosilane in anhydrous ethanol, then slowly add deionized water to obtain a vinyldimethylfluorosilane hydrolysate. A3. Under nitrogen protection, the vinyl dimethyl fluorosilane hydrolysate is added dropwise to the nano silicon nitride suspension, and the mixture is magnetically stirred until homogeneous. The reaction is carried out at 50-70℃ for 2-3 hours. A4. After the reaction is complete, the solvent is removed by rotary evaporation to obtain vinyl dimethyl fluorosilane modified nano silicon nitride.

4. The anti-leakage pulp layer paper according to claim 3, characterized in that: The amount of vinyldimethylfluorosilane added is 3-15% of the mass of nano-silicon nitride.

5. The anti-leakage pulp layer paper according to claim 1, characterized in that: The method for preparing the modified starch includes the following steps: B1. Mix starch and water in a mass ratio of 1:3-5 until they are completely dispersed and free of granules. Then, heat the mixture to 85-95℃ and stir at low speed for 30-40 minutes to obtain gelatinized starch. B2. Lower the system temperature to 70-75℃ and adjust the pH to 6-7. Then add α-amylase and perform the first enzymatic hydrolysis reaction for 60-90 minutes to obtain short-chain starch. B3. Lower the system temperature to 55-60℃ and adjust the pH to 4.5-5.

5. Then add glucoamylase and perform a second enzymatic hydrolysis reaction for 90-120 min to obtain refined starch. B4. Lower the system temperature to 45-55℃ and adjust the pH to 6.5-7.

5. Then add the compound enzyme and perform the third enzymatic hydrolysis reaction for 120-180 min. Next, raise the temperature to 95-100℃ for inactivation treatment for 10-15 min. Centrifuge, dehydrate, wash, dry and pulverize to obtain modified starch of 100-200 mesh.

6. The anti-leakage pulp layer paper according to claim 5, characterized in that: The amount of α-amylase added is 0.1-0.3% of the starch mass; the amount of glucoamylase added is 0.2-0.5% of the starch mass; and the amount of the compound enzyme added is 0.1-0.2% of the starch mass.

7. The anti-leakage pulp layer paper according to claim 5, characterized in that: The complex enzyme is a decarboxylase and an oxidative dehydrogenase, wherein the decarboxylase and the oxidative dehydrogenase are mixed in a mass ratio of 1:1.8-2.

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8. The anti-leakage pulp layer paper according to claim 1, characterized in that: The method for preparing the dense core layer includes the following steps: C1. Mix softwood pulp and polypropylene fiber according to the specified ratio, put them into a high-consistency pulper, adjust the fiber length to 0.8-1.2mm, add deionized water, and prepare a mixed fiber pulp with a fiber mass concentration of 18-22% for later use. C2. Mix the modified starch and water at a mass ratio of 1:3-5, heat to 85-90℃ and keep warm for 30 minutes to fully gelatinize until there are no particles and the mixture is fluid and uniform. Cool down to 55-60℃ and set aside. C3. Mix the mixed fiber slurry from step C1, vinyl dimethyl fluorosilane modified nano-silicon nitride, fumed silica, and gelatinized modified starch from step C2. After stirring evenly, heat to 65-70℃, add the mixed monomers, initiator, and crosslinking agent in sequence, and continue stirring at low speed for 30-45 minutes. After the reaction is completed, adjust the solid content of the slurry to 25%-30% to obtain a dense core layer molding slurry. C4. Feed the dense core layer forming slurry from step C3 into the inclined wire paper machine, control the paper machine speed to 15-20m / min, and pass through the forming, pressing and pre-drying processes in sequence to obtain the dense core layer.

9. A method for preparing the anti-leakage pulp layer paper as described in any one of claims 1-8, characterized in that: Includes the following steps: S1. Fix the dense core paper and apply a water-based anti-corrosion emulsion of phosphate ester to its outer side using a micro-gravure coating method at a coating speed of 20-25 m / min. After coating, put it into an oven and dry at 65-70℃ for 10-15 min to form an anti-corrosion coating on the outer side of the dense core paper. S2. Turn the base paper with the anti-corrosion coating over and apply PVDF aqueous dispersion to the inner side of the core layer using a doctor blade coating method at a coating speed of 18-22 m / min. After coating, dry at 70-75℃ for 15-20 min to solidify and form an impermeable surface layer on the inner side of the dense core layer base paper, thus obtaining the leak-proof pulp layer paper.

10. The application of the leak-proof pulp layer paper as described in any one of claims 1-8 in carbon-zinc batteries, characterized in that: The anti-corrosion coating is used to adhere to one side of the zinc cylinder, and the impermeable surface layer is used to contact the positive electrode carbon powder.

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