Paper-wrapped copper flat wire and preparation method and application thereof

Abstract

The invention discloses a paper-covered copper flat wire and a preparation method and application thereof, belongs to the technical field of insulated wires, and is used for solving the technical problem that the insulating property, flame retardant property and high temperature resistance of a paper-covered copper flat wire in the prior art need to be further improved. Wood pulp fibers, the pretreated PI fibers and purified water are added into a dissociator to be dissociated, and dissociated pulp is obtained. The insulation paper with high insulation, high tensile strength, flame retardance and high temperature resistance, which is prepared by coating phosphorus-aluminum gel on an insulation paper crude product prepared by taking polysiloxane emulsion, pretreated PI fiber and wood pulp fiber as base materials, is tightly coated on the copper flat wire in an adhesive bonding manner, so that stable insulation paper coating is formed on the copper flat wire; and the insulating property and the high-temperature aging resistance are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of insulated wire processing, and particularly relates to a paper-covered copper flat wire, a preparation method thereof, and an application thereof. Background Art

[0002] As a key device in the power system, dry-type transformers have been widely used in places with high fire protection requirements such as subway, high-rise buildings, workshops, and power stations due to their advantages of not requiring oil immersion, good fire protection performance, environmental protection and safety. Compared with oil-immersed transformers, dry-type transformers use air as the insulating and cooling medium, but their insulation performance and heat dissipation capacity are relatively poor, resulting in more consumption of effective materials.

[0003] Copper flat wire is a key material for transformer windings, and its performance directly affects the efficiency, safety, and service life of transformers. Traditional copper flat wires mostly use ordinary insulating paint or synthetic resin coatings as the insulating layer, which have problems such as poor environmental protection, insufficient high-temperature resistance, and complex processes. Paper insulation is a new way to insulate copper flat wires.

[0004] However, when the paper-covered copper flat wire in the prior art is prepared, the insulating paper is usually directly coated on the outside of the copper flat wire, and the adhesion between the insulating paper and the copper conductor is poor. During the operation of the transformer, stratification is likely to occur due to electromagnetic vibration, thermal expansion and contraction, etc., resulting in partial discharge or even insulation failure. Although common insulating papers have good insulation performance, they are essentially a kind of fiber material with poor flame retardancy, and it is difficult to effectively suppress the spread of fire in case of short circuit or overload, posing a fire hazard. Moreover, the insulating paper is prone to thermal aging in a high-temperature environment, resulting in a decline in the insulation performance of the paper-covered copper flat wire. Summary of the Invention

[0005] The purpose of the present invention is to provide a paper-covered copper flat wire, a preparation method thereof, and an application thereof, which are used to solve the technical problems that the insulation performance, flame retardancy, and high-temperature resistance of the paper-covered copper flat wire in the prior art need to be further improved.

[0006] The purpose of the present invention can be achieved by the following technical solutions: A preparation method of a paper-covered copper flat wire includes the following steps:

[0007] S1. Dissociate and disperse the wood pulp board to prepare wood pulp fibers, and add the wood pulp fibers, pretreated PI fibers, and purified water into a dissociator for dissociation to obtain a dissociated slurry;

[0008] S2. Mix the dissociated slurry and polydimethylsiloxane emulsion, stir and mix for 20 - 30 min to obtain a papermaking slurry, and the papermaking slurry is subjected to sheet-making to obtain a crude insulating paper with a thickness of 0.9 - 1.1 mm;

[0009] S3. After uniformly coating the crude insulating paper with silica-aluminum gel, hot-rolling is carried out using a hot-rolling machine at a temperature of 110 - 120 °C to obtain the insulating paper;

[0010] S4. After coating the insulating paper with an epoxy resin adhesive, uniformly winding it around a flat copper wire, and then carrying out a heat curing treatment on it to prepare a paper-covered flat copper wire.

[0011] Furthermore, in step S1, the dosage ratio of the wood pulp fiber, the pretreated PI fiber, and purified water is 2 g: 1 g: 150 mL; in step S2, the volume ratio of the dissociated pulp to the polysiloxane emulsion is 7: 1; in step S3, the coating amount of the silica-aluminum gel is 10 g / m²; in step S4, the epoxy resin adhesive is composed of epoxy resin E-42 and 4-aminobutyltriethoxysilane in a weight ratio of 5: 1.

[0012] Furthermore, the pretreated PI fiber is processed by the following steps:

[0013] A1. Mix and stir the polyimide short fiber and the activation liquid, raise the temperature of the reaction system to 50 - 60 °C, carry out heat preservation treatment for 40 - 60 min, and perform post-treatment to obtain activated PI fiber;

[0014] A2. Mix and stir the activated PI fiber and acetic acid solution, react at room temperature for 90 - 120 min, and perform post-treatment to obtain the pretreated PI fiber.

[0015] The synthesis reaction mechanism of the pretreated PI fiber is as follows:

[0016] During the reaction process, the hydroxide ion combines with the carbonyl carbon atom to form a tetrahedral intermediate. Then, the proton on the imide nitrogen atom in the intermediate is taken away by the alkaline environment to form a negative ion. Subsequently, an elimination reaction occurs, the imide ring opens, and molecular fragments with carboxylate ions (or their precursors) and amino groups are generated. N,N-dimethylacetamide, as a polar aprotic solvent, can dissolve the intermediate products and products generated by the reaction, promote the reaction, and can stabilize the negative ion intermediate during the reaction process, reducing the activation energy of the reaction; the amino group on the PI fiber, as a basic group, is prone to accepting hydrogen ions to form ammonium ions. At the same time, there are carboxylate ion precursors or unstable intermediates generated after the opening of the imide ring on the activated PI fiber, which will further undergo a protonation reaction under acidic conditions to form stable carboxyl groups, and the pretreated PI fiber modified with carboxyl reaction active sites is prepared.

[0017] Further, in step A1, the solid-liquid ratio of the polyimide short fibers to the activation liquid is 1:10. The activation liquid consists of sodium hydroxide, purified water, and N,N-dimethylacetamide in a ratio of 1 g:10 mL:15 mL. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, followed by suction filtration. The filter cake is washed with purified water until neutral and then dried by suction. The filter cake is transferred to a drying oven at 70°C and dried to a constant weight to obtain activated PI fibers. In step A2, the solid-liquid ratio of the activated PI fibers to the acetic acid solution is 1:8. The acetic acid solution consists of glacial acetic acid and purified water in a ratio of 1 g:5 mL. The post-treatment includes: after the reaction is completed, suction filtration is carried out. The filter cake is washed with purified water until neutral and then dried by suction. The filter cake is transferred to a drying oven at 70°C and dried to a constant weight to obtain pretreated PI fibers.

[0018] Further, the polysiloxane emulsion is prepared by the following steps:

[0019] B1. Mix diethoxysilane-modified DOPO, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methacryloyloxytrimethylsiloxane to obtain a mixed siloxane solution.

[0020] B2. While stirring, drop the mixed siloxane solution into an emulsion at a temperature of 60 - 80°C. After the dropping is complete, carry out heat preservation treatment for 60 - 80 min, then reduce the temperature of the reaction system to room temperature, and adjust the pH of the reaction system to 7 to obtain the polysiloxane emulsion.

[0021] The synthesis reaction mechanism of the polysiloxane emulsion is as follows:

[0022] During the reaction, the mixed siloxane solution is emulsified and dispersed in the emulsion. At the same time, the protonic acid in the emulsion catalyzes the hydrolysis of the cyclic siloxane monomers or siloxane ethane bonds in the mixed siloxane solution to form siloxane chain segments with silanol activity. Then, the silanols undergo condensation to form a polysiloxane emulsion with a polysiloxane chain segment modified with epoxy groups, unsaturated olefin double bonds, and DOPO.

[0023] Further, in step B1, the weight ratio of diethoxysilane-modified DOPO, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methacryloyloxytrimethylsiloxane is 3 - 4:2 - 3:8 - 9:1 - 2. In step B2, the volume ratio of the mixed siloxane solution to the emulsion is 1:20. The emulsion consists of anhydrous ethanol, purified water, 80 wt% sulfuric acid, sodium dodecyl sulfate, Tween - 80, and polyethylene glycol - 400 in a ratio of 30 mL:90 mL:8 mL:1 g:2 g:2 g.

[0024] Furthermore, the preparation method of diethoxysilane-modified DOPO is as follows: Under an inert atmosphere, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide, 3-isocyanatopropylmethyldiethoxysilane, and 1,4-dioxane are mixed and stirred. The temperature of the reaction system is raised to 50 - 60 °C, and the reaction is carried out under insulation for 80 - 90 min. After post-treatment, diethoxysilane-modified DOPO is obtained.

[0025] The synthesis reaction mechanism of diethoxysilane-modified DOPO is as follows:

[0026] During the reaction process, the hydroxyl group on the molecule of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide reacts with the isocyanate group on the molecule of 3-isocyanatopropylmethyldiethoxysilane to form DOPO modified with diisocyanate groups. The mass spectrometry analysis data of it are: m / z: 463.15800 (100.0%), 464.16136 (23.8%), 464.15757 (5.1%), 465.15484 (3.3%), 465.16471 (2.7%), 465.16225 (1.2%), 465.16092 (1.2%).

[0027] Furthermore, the dosage ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide to 3-isocyanatopropylmethyldiethoxysilane is 1 mol:1 mol, and the dosage ratio of 3-isocyanatopropylmethyldiethoxysilane to 1,4-dioxane is 1 g:6 mL. The post-treatment includes: After the reaction is completed, the temperature of the reaction system is raised to 70 - 80 °C, and the low-boiling substances are removed by reduced pressure distillation to obtain diethoxysilane-modified DOPO.

[0028] Furthermore, the preparation method of the phosphorus-aluminum gel is as follows: Phosphoric acid is heated to 80 - 90 °C, and aluminum hydroxide is added to phosphoric acid in batches. The reaction is carried out under insulation for 2 - 3 h. The temperature of the reaction system is cooled to room temperature, and 5-hexenyltriethoxysilane and an initiator are added to the reaction system, and the reaction is carried out for 40 - 60 min to obtain the phosphorus-aluminum gel.

[0029] The synthesis reaction mechanism of the phosphorus-aluminum gel is as follows:

[0030] During the reaction process, phosphoric acid reacts with aluminum hydroxide to generate amorphous aluminum phosphate and water. The surface of the generated amorphous aluminum phosphate contains unreacted P-OH and Al-OH, which further condense to form a three-dimensional network porous gel under a heating environment. In an acidic environment, the ethoxy groups of 5-hexenyltriethoxysilane are hydrolyzed into silanols and chemically crosslinked with the surface of the porous gel. Ammonium persulfate is used as a free radical initiator and is uniformly dispersed as it dissolves in the aqueous solution to prepare the phosphorus-aluminum gel.

[0031] Furthermore, the molar ratio of phosphoric acid to aluminum hydroxide is 3:2, the weight ratio of aluminum hydroxide, 5-hexenyltriethoxysilane and the initiator is 3:1:0.1, the initiator is ammonium persulfate, and the mass fraction of phosphoric acid is 50%.

[0032] The present invention also provides a paper-covered copper flat wire, which is prepared by using the preparation method of a paper-covered copper flat wire described above.

[0033] An application of a paper-covered copper flat wire, wherein the paper-covered copper flat wire prepared by using the preparation method of a paper-covered copper flat wire described above is applied to a dry-type transformer.

[0034] The present invention has the following beneficial effects:

[0035] 1. In the present invention, an insulating paper is bonded to the outside of a copper flat wire through an adhesive to form an insulating coating. Under the action of high temperature, while the adhesive cures and crosslinks, it promotes the crosslinking bonding between the adhesive, the insulating paper and the surface layer of the copper flat wire, forming a stable insulating paper coating on the outside of the copper flat wire, reducing the porosity of the paper-covered insulating layer outside the paper-covered copper flat wire, thereby effectively reducing the penetration of moisture, improving the insulation performance of the paper-covered copper flat wire. When the insulating paper is prepared, the mixed pulp of PI fiber and pulp fiber is strengthened by a polysiloxane emulsion, and then paper is made after dilution. The PI fiber retains the rigid aromatic ring structure of polyimide. The high modulus of its molecular chain provides a skeleton support for the paper base, inhibits the slippage of molecular chains under external force, and improves the tensile strength of the paper. Moreover, the dielectric constant of the PI fiber is low, the main chain contains imide five-membered rings and aromatic rings, and the decomposition temperature is high, which cooperates with the high stability of the polysiloxane to further improve the high-temperature resistance and electrical insulation performance of the material.

[0036] 2. After the polyimide fiber is activated and then re-treated with acetic acid in the present invention, a large number of carboxyl groups are formed on the PI fiber, improving its reactivity, promoting the uniform dispersion and mixing of the pretreated PI fiber in the papermaking pulp and wood pulp fiber. The polysiloxane molecules in the polysiloxane emulsion form a polysiloxane network between the fibers, and the epoxy groups on the polysiloxane molecular chain can undergo condensation with the oxygen-containing active sites on the surface of the pretreated PI fiber or wood pulp fiber, promoting the crosslinking bonding between the PI fiber and the wood pulp fiber in the insulating paper, thereby further improving the tensile strength of the insulating paper. The Si-O bond energy of the polysiloxane main chain is high and the electron trap is deep, thereby inhibiting the conduction current. The phosphaphenanthrene ring in DOPO modified on the polysiloxane molecule contains a large π-conjugated system and a P=O polar bond, which can capture high-energy electrons and scatter the electron path, improving the local breakdown voltage and further improving the insulation performance of the material.

[0037] 3. The present invention also prepares a gel from phosphoric acid and aluminum hydroxide, mixes it with 5-hexenyltriethoxysilane and an initiator to form a phosphorus-aluminum gel, coats the phosphorus-aluminum gel on insulating paper, and after high-temperature and high-pressure treatment, the initiator initiates the free-radical polymerization of the unsaturated double bonds on the phosphorus-aluminum gel and the unsaturated olefins on the crude insulating paper, stably attaching the phosphorus-aluminum gel to the crude insulating paper in the form of a C-C covalent bond network, enhancing the van der Waals force and mechanical interlocking. The phosphorus-aluminum gel has a structure of silicone-encapsulated amorphous aluminum phosphate, which improves the electron tunneling barrier. Then, through hot rolling, it promotes the filling of the pores between fibers by the phosphorus-aluminum gel, eliminates the interface energy level defects, forms a densification effect, and improves the tensile strength and insulation performance of the insulating paper material. The phosphorus-aluminum gel pyrolyzes under high-temperature action, increases the flame retardancy of the insulating paper through condensed-phase catalytic carbon formation and gas-phase free-radical quenching. Moreover, the synergistic effect between the phosphorus-aluminum gel and polysiloxane is enhanced to further improve its flame retardancy. In the insulating paper, the phosphorus-aluminum gel and polysiloxane undergo intermolecular recombination at high temperature to form Si-O-Al bonds to replace organic bonds, resisting thermal cracking and further improving its heat stability. Detailed Embodiments

[0038] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] In the present invention, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide has a CAS number of 35948-26-6;

[0040] In the present invention, the polyimide short fibers are selected from Jiangsu Xiannuo New Materials Technology Co., Ltd., with the brand of Zhenlun Shilon and the model of S0T-S;

[0041] In the present invention, the wood pulp board is selected from Henan Huining Paper Co., Ltd., using perennial northern coniferous wood as the raw material, and the fiber length is 1 - 2.95 mm;

[0042] In the present invention, the epoxy value of epoxy resin E-42 is 0.38 - 0.45 eq / 100 g.

[0043] Example 1

[0044] This example provides a preparation method of a polysiloxane emulsion, including the following steps:

[0045] Step 1. Prepare diethoxysilane-modified DOPO

[0046] Weigh: 24.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide, 21.7 g of 3-isocyanatopropylmethyldiethoxysilane and 130.2 mL of 1,4-dioxane were added to a reaction flask protected by argon and mixed and stirred. The temperature of the reaction flask was raised to 50 °C, and the reaction was carried out for 80 min while maintaining the temperature. Then the temperature of the reaction flask was raised to 70 °C, and the low-boiling substances were removed by distillation under reduced pressure to obtain diethoxysilane-modified DOPO.

[0047] Step 2: Prepare a mixed siloxane solution

[0048] Mix 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methylpropenyltrisiloxane in a weight ratio of 3:2:8:1 to obtain a mixed siloxane solution.

[0049] Step 3: Prepare a polysiloxane emulsion

[0050] Mix 30 mL of absolute ethanol, 90 mL of purified water, 8 mL of 80 wt% sulfuric acid, 1 g of sodium dodecyl sulfate, 2 g of Tween-80, and 2 g of polyethylene glycol-400 to obtain an emulsion;

[0051] Weigh: Add 2 L of the emulsion to a reaction flask and stir. Set the stirring rate to 800 rpm. Raise the temperature of the reaction flask to 60 °C. Add 100 mL of the mixed siloxane solution dropwise to the reaction flask. After the addition is complete, maintain the temperature for 60 min. Then lower the temperature of the reaction flask to room temperature and adjust the pH of the reaction system to 7 to obtain a polysiloxane emulsion.

[0052] Example 2

[0053] This example provides a method for preparing a polysiloxane emulsion, which includes the following steps:

[0054] Step 1: Prepare diethoxysilane-modified DOPO

[0055] Weigh: 24.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide, 21.7 g of 3-isocyanatopropylmethyldiethoxysilane and 130.2 mL of 1,4-dioxane were added to a reaction flask protected by argon and mixed and stirred. The temperature of the reaction flask was raised to 55 °C, and the reaction was carried out for 85 min while maintaining the temperature. Then the temperature of the reaction flask was raised to 75 °C, and the low-boiling substances were removed by distillation under reduced pressure to obtain diethoxysilane-modified DOPO.

[0056] Step 2: Prepare a mixed siloxane solution

[0057] Mix 3.5:2.5:8.5:1.5 by weight of diethoxysilane-modified DOPO, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methylpropenoic acid trioxane cyclotrisiloxane uniformly to obtain a mixed siloxane solution.

[0058] Step 3: Prepare a polysiloxane emulsion

[0059] Mix 30 mL of absolute ethanol, 90 mL of purified water, 8 mL of 80 wt% sulfuric acid, 1 g of sodium dodecyl sulfate, 2 g of Tween-80, and 2 g of polyethylene glycol-400 uniformly to obtain an emulsion;

[0060] Weigh: Add 2 L of the emulsion to a reaction flask and stir. Set the stirring rate to 800 rpm. Raise the temperature of the reaction flask to 70 °C. Add 100 mL of the mixed siloxane solution dropwise to the reaction flask. After the addition is complete, perform a heat preservation treatment for 70 min. Lower the temperature of the reaction flask to room temperature. Adjust the pH of the reaction system to 7 to obtain a polysiloxane emulsion.

[0061] Example 3

[0062] This example provides a method for preparing a polysiloxane emulsion, which includes the following steps:

[0063] Step 1: Prepare diethoxysilane-modified DOPO

[0064] Weigh: Add 24.6 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 21.7 g of 3-isocyanatopropylmethyldiethoxysilane, and 130.2 mL of 1,4-dioxane to a reaction flask protected by argon and mix and stir. Raise the temperature of the reaction flask to 60 °C and perform a heat preservation reaction for 90 min. Raise the temperature of the reaction flask to 80 °C and distill off the low-boiling substances under reduced pressure to obtain diethoxysilane-modified DOPO.

[0065] Step 2: Prepare a mixed siloxane solution

[0066] Mix 4:3:9:2 by weight of diethoxysilane-modified DOPO, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methylpropenoic acid trioxane cyclotrisiloxane uniformly to obtain a mixed siloxane solution.

[0067] Step 3: Prepare a polysiloxane emulsion

[0068] Mix 30 mL of absolute ethanol, 90 mL of purified water, 8 mL of 80 wt% sulfuric acid, 1 g of sodium dodecyl sulfate, 2 g of Tween-80, and 2 g of polyethylene glycol-400 uniformly to obtain an emulsion;

[0069] Weigh: Add 2 L of the emulsion into a reaction flask and stir. Set the stirring rate to 800 rpm. Raise the temperature of the reaction flask to 80 °C. Dropwise add 100 mL of the mixed siloxane solution into the reaction flask. After the addition is complete, conduct heat preservation treatment for 80 min. Lower the temperature of the reaction flask to room temperature. Adjust the pH of the reaction system to 7 to obtain a polysiloxane emulsion.

[0070] Example 4

[0071] This example provides a method for preparing a paper-covered copper flat wire, which includes the following steps:

[0072] S1. Prepare pretreated PI fibers

[0073] Mix sodium hydroxide, purified water, and N,N-dimethylacetamide evenly at a ratio of 1 g:10 mL:15 mL to obtain an activation solution;

[0074] Weigh: Add polyimide short fibers and the activation solution into a reaction flask at a solid-liquid ratio of 1:10, mix and stir. Raise the temperature of the reaction flask to 50 °C, conduct heat preservation treatment for 40 min. Lower the temperature of the reaction flask to room temperature, perform suction filtration. Wash the filter cake with purified water until it is neutral and then drain it. Transfer the filter cake to a drying oven at 70 °C and dry it to constant weight to obtain activated PI fibers;

[0075] Mix glacial acetic acid and purified water evenly at a ratio of 1 g:5 mL to obtain an acetic acid solution;

[0076] Weigh: Add the activated PI fibers and the acetic acid solution into a reaction flask at a solid-liquid ratio of 1:8, mix and stir. Stir at room temperature for 90 min, perform suction filtration. Wash the filter cake with purified water until it is neutral and then drain it. Transfer the filter cake to a drying oven at 70 °C and dry it to constant weight to obtain pretreated PI fibers.

[0077] S2. Prepare dissociating pulp

[0078] Mix wood pulp board and deionized water at a ratio of 1 g:100 mL, soak at room temperature for 6 h. Transfer it to a beater, set the rotation speed to 2000 rpm, beat for 6 min, and then transfer it to a high-frequency refiner to obtain a beating degree of 43 °SR. After filtration and drying, obtain wood pulp fibers;

[0079] Add the wood pulp fibers, pretreated PI fibers, and purified water into a high-frequency dissociator at a ratio of 2 g:1 g:150 mL. Connect the power supply, reset the rotation counter of the dissociator to zero, and then start dissociating the pulp. When the counter shows 1000 revolutions, disconnect the power supply. After 1 min, continue to energize until the rotation reaches 10,000 revolutions, disconnect the power supply. After 1 min, continue to energize until the rotation reaches 30,000 revolutions, and then disconnect the power supply to obtain dissociating pulp.

[0080] S3. Prepare the crude insulation paper

[0081] Dissociate the slurry and the polysiloxane emulsion prepared in Example 1 were added to a stirrer in a volume ratio of 7:1, the stirring speed was set at 300 rpm, and stirred and mixed for 20 min to obtain papermaking pulp;

[0082] Transfer the papermaking pulp to a sheet former, dilute it with water to obtain a suspension with a concentration of 0.02 wt%, dehydrate it by oil pressure and then dry it to obtain a crude insulating paper with a thickness of 0.9 mm.

[0083] S4. Prepare insulating paper

[0084] Weigh: 500 mL of 50 wt% phosphoric acid solution was added to a reaction flask and stirred. The temperature of the reaction flask was raised to 80 °C. 132.7 g of nano-aluminum hydroxide was added to the reaction flask in batches, and the reaction was carried out at a constant temperature for 2 h. The temperature of the reaction flask was lowered to room temperature. 44.2 g of 5-hexenyltriethoxysilane and 4.4 g of initiator ammonium persulfate were added to the reaction flask, and the reaction was carried out for 40 min to obtain a phosphorus-aluminum gel;

[0085] According to the coating amount of 10 g / m 2 The silicon-aluminum gel was respectively coated on both sides of the crude insulating paper, and it was hot-rolled by a hot rolling machine at a temperature of 110 °C, a pressure of 60 N / mm 2 and a rolling speed of 3 m / min to obtain insulating paper.

[0086] S5. Prepare paper-covered copper flat wire

[0087] Epoxy resin E-42 and 4-aminobutyltriethoxysilane were mixed in a weight ratio of 5:1 to obtain an epoxy resin adhesive for standby;

[0088] The epoxy resin adhesive was coated on one side of the insulating paper at a coating amount of 20 g / m 2 . After it was evenly wound around the copper flat wire, it was transferred to an environment at a temperature of 150 °C and cured at a constant temperature for 30 min to obtain a paper-covered copper flat wire.

[0089] Example 5

[0090] This example provides a method for preparing a paper-covered copper flat wire, including the following steps:

[0091] S1. Prepare pretreated PI fiber

[0092] Sodium hydroxide, purified water and N,N-dimethylacetamide were mixed evenly in a ratio of 1 g:10 mL:15 mL to obtain an activation solution;

[0093] Weigh: Add polyimide short fibers and the activation solution into a reaction flask at a solid-liquid ratio of 1:10, mix and stir. Raise the temperature of the reaction flask to 55 °C, keep it warm for 50 min, then lower the temperature of the reaction flask to room temperature, carry out suction filtration. Wash the filter cake with purified water until it is neutral and then drain it. Transfer the filter cake to a drying oven at 70 °C and dry it to a constant weight to obtain activated PI fibers;

[0094] Mix glacial acetic acid and purified water at a ratio of 1 g:5 mL to obtain an acetic acid solution;

[0095] Weigh: Add activated PI fibers and the acetic acid solution into a reaction flask at a solid-liquid ratio of 1:8, mix and stir, and stir at room temperature for 105 min. Carry out suction filtration. Wash the filter cake with purified water until it is neutral and then drain it. Transfer the filter cake to a drying oven at 70 °C and dry it to a constant weight to obtain pretreated PI fibers.

[0096] S2. Prepare the dissociation slurry

[0097] Mix wood pulp board and deionized water at a ratio of 1 g:100 mL, soak it at room temperature for 7 h, transfer it to a beater, set the rotation speed to 2000 rpm, beat for 7 min, and then transfer it to a high-frequency refiner to obtain a beating degree of 45 °SR. After filtration and drying, obtain wood pulp fibers;

[0098] Add wood pulp fibers, pretreated PI fibers, and purified water into a high-frequency dissociator at a ratio of 2 g:1 g:150 mL, turn on the power, reset the rotation counter of the dissociator to zero, and then start dissociating the pulp. When the counter shows 1000 revolutions, turn off the power. After 1 min, turn on the power again until the number of revolutions reaches 10,000, turn off the power. After 1 min, turn on the power again until the number of revolutions reaches 30,000, and then turn off the power to obtain the dissociation slurry.

[0099] S3. Prepare the crude insulating paper

[0100] Add the dissociation slurry and the polysiloxane emulsion prepared in Example 2 into a stirrer at a volume ratio of 7:1, set the stirring speed to 350 rpm, and stir and mix for 25 min to obtain the papermaking slurry;

[0101] Transfer the papermaking slurry to a sheet former, dilute it with water to obtain a suspension with a concentration of 0.02 wt%, and dry it after oil pressure dewatering to obtain a crude insulating paper with a thickness of 1.0 mm.

[0102] S4. Prepare the insulating paper

[0103] Weigh: Add 500 mL of 50 wt% phosphoric acid solution into a reaction flask and stir. Raise the temperature of the reaction flask to 85 °C. Add 132.7 g of nano-aluminum hydroxide to the reaction flask in batches, keep the temperature for reaction for 2.5 h, cool the reaction flask to room temperature, add 44.2 g of 5-hexenyltriethoxysilane and 4.4 g of initiator ammonium persulfate to the reaction flask, and react for 50 min to obtain a phosphorus-aluminum gel;

[0104] According to the coating amount of 10 g / m 2 Coat the silicon-aluminum gel on both sides of the crude insulating paper respectively, and hot-roll it with a hot-rolling machine at a temperature of 115 °C, a pressure of 70 N / mm 2 and a rolling speed of 4 m / min to obtain an insulating paper.

[0105] S5. Prepare a paper-covered copper flat wire

[0106] Mix epoxy resin E-42 and 4-aminobutyltriethoxysilane in a weight ratio of 5:1 to obtain an epoxy resin adhesive for standby;

[0107] Coat the epoxy resin adhesive on one side of the insulating paper according to the coating amount of 20 g / m 2 After evenly winding it on the copper flat wire, transfer it to an environment at a temperature of 160 °C and keep the temperature for curing for 40 min to obtain a paper-covered copper flat wire.

[0108] Example 6

[0109] This example provides a method for preparing a paper-covered copper flat wire, including the following steps:

[0110] S1. Prepare pretreated PI fibers

[0111] Mix sodium hydroxide, purified water and N,N-dimethylacetamide evenly in a ratio of 1 g:10 mL:15 mL to obtain an activation solution;

[0112] Weigh: Add polyimide short fibers and the activation solution into a reaction flask according to a solid-liquid ratio of 1:10, mix and stir. Raise the temperature of the reaction flask to 60 °C, keep the temperature for treatment for 60 min, lower the temperature of the reaction flask to room temperature, filter by suction, wash the filter cake with purified water until it is neutral and then drain it by suction. Transfer the filter cake to a drying oven at a temperature of 70 °C and dry it to constant weight to obtain activated PI fibers;

[0113] Mix glacial acetic acid and purified water evenly in a ratio of 1 g:5 mL to obtain an acetic acid solution;

[0114] Weigh: Add the activated PI fibers and the acetic acid solution into a reaction flask according to a solid-liquid ratio of 1:8, mix and stir, stir at room temperature for 120 min, filter by suction, wash the filter cake with purified water until it is neutral and then drain it by suction. Transfer the filter cake to a drying oven at a temperature of 70 °C and dry it to constant weight to obtain pretreated PI fibers.

[0115] S2. Prepare the dissociation slurry

[0116] Mix wood pulp board and deionized water at a ratio of 1 g:100 mL, soak at room temperature for 8 h, transfer it to a beater, set the rotation speed to 2000 rpm, beat for 8 min, then transfer it to a high-frequency refiner to obtain a beating degree of 46°SR. After filtration and drying, wood pulp fibers are obtained;

[0117] Add wood pulp fibers, pretreated PI fibers, and purified water at a ratio of 2 g:1 g:150 mL to a high-frequency dissociator, turn on the power, reset the rotation counter of the dissociator to zero, and then start dissociating the pulp. When the counter shows 1000 revolutions, turn off the power. After 1 min, turn on the power again until the rotation reaches 10,000 revolutions, turn off the power. After 1 min, turn on the power again until the rotation reaches 30,000 revolutions, and then turn off the power to obtain the dissociation slurry.

[0118] S3. Prepare the crude insulating paper

[0119] Add the dissociation slurry and the polysiloxane emulsion prepared in Example 3 to a stirrer at a volume ratio of 7:1 and mix, set the stirring speed to 400 rpm, and stir and mix for 30 min to obtain the papermaking slurry;

[0120] Transfer the papermaking slurry to a sheet former, dilute it with water to obtain a suspension with a concentration of 0.02 wt%, and dry it after oil pressure dewatering to obtain a crude insulating paper with a thickness of 1.1 mm.

[0121] S4. Prepare the insulating paper

[0122] Weigh: Add 500 mL of 50 wt% phosphoric acid solution to a reaction flask and stir. The temperature of the reaction flask rises to 90 °C. Add 132.7 g of nano-aluminum hydroxide to the reaction flask in batches, keep the reaction for 3 h, cool the reaction flask to room temperature, add 44.2 g of 5-hexenyltriethoxysilane and 4.4 g of initiator ammonium persulfate to the reaction flask, and react for 60 min to obtain the phosphorus-aluminum gel;

[0123] According to the coating amount of 10 g / m 2 Coat the silicon-aluminum gel on both sides of the crude insulating paper respectively, and hot-roll it with a hot-rolling machine at a temperature of 120 °C, a pressure of 80 N / mm 2 and a rolling speed of 5 m / min to obtain the insulating paper.

[0124] S5. Prepare the paper-covered copper flat wire

[0125] Mix epoxy resin E-42 and 4-aminobutyltriethoxysilane at a weight ratio of 5:1 to obtain the epoxy resin adhesive for standby;

[0126] Apply the epoxy resin adhesive at 20 g / m 2The coating amount is coated on one side of the insulating paper. After evenly winding it around the flat copper wire, it is transferred to an environment with a temperature of 170 °C and cured for 50 minutes to obtain a paper-covered flat copper wire.

[0127] Comparative Example 1

[0128] The difference between this comparative example and Example 6 is that in the preparation process of the polysiloxane emulsion used, in Step 2, diethoxysilane-modified DOPO was not added.

[0129] Comparative Example 2

[0130] The difference between this comparative example and Example 6 is that Step S1 was cancelled, and polyimide short fibers were used to replace the pretreated PI fibers in Step 2.

[0131] Comparative Example 3

[0132] The difference between this comparative example and Example 6 is that in Step S3, the polysiloxane emulsion was not added.

[0133] Comparative Example 4

[0134] The difference between this comparative example and Example 6 is that in Step S4, 5-hexenyltriethoxysilane and the initiator were not added.

[0135] Performance Test:

[0136] Referring to the standard QB / T 4250-2011 "Interturn Insulating Paper for 500 kV Transformers", the longitudinal tensile strength and power frequency breakdown voltage of the insulating paper specimens prepared in Examples 1-3 and Comparative Examples 1-4 were measured;

[0137] Referring to the standard GB / T 14656-2009 "Test Method for Combustion Performance of Flame Retardant Papers and Boards", the average afterflame time of the insulating paper specimens prepared in Examples 1-3 and Comparative Examples 1-4 was measured;

[0138] The insulating paper specimens prepared in Examples 1-3 and Comparative Examples 1-4 were placed in an environment with a temperature of 200 °C for 60 days of thermal aging, and their tensile strength, power frequency breakdown voltage, and average afterflame time were measured. The specific test results are shown in Table 1 below.

[0139] Table 1 - Data Sheet of Performance Detection of Specimens

[0140]

[0141] Data Analysis:

[0142] Comparing and analyzing the data in Table 1 above, the longitudinal tensile strength of the insulating paper sample prepared by the present invention reaches 1013 kN / m, the power frequency breakdown voltage reaches 10.921 kV / mm, and the average afterglow time is reduced to 2.0 s. After heat aging treatment, the longitudinal tensile strength of the insulating paper sample reaches 9.58 kN / m, the power frequency breakdown voltage reaches 10.723 kV / mm, and the average afterglow time is maintained at 2.6 s. All the performance test data are superior to those of the comparative example. This shows that by coating the crude insulating paper prepared by reinforcing pretreated PI fibers and wood pulp fibers with polysiloxane emulsion with phosphoaluminum gel, the present invention not only effectively improves the insulation performance and tensile strength of the insulating paper, but also improves its flame retardant performance and heat aging resistance. Then, the prepared insulating paper is tightly coated on the flat copper wire with an adhesive to form a stable insulating paper coating on the flat copper wire, improving its insulation performance and high temperature aging resistance.

[0143] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A preparation method of a paper-covered copper flat wire, characterized in that, It includes the following steps: S1. Dissociate and disperse the wood pulp board to prepare wood pulp fibers. Add the wood pulp fibers, pretreated PI fibers, and purified water into a dissociator for dissociation to obtain a dissociated slurry; S2. Mix the dissociated slurry and the polysiloxane emulsion, stir and mix for 20 - 30 min to obtain a papermaking slurry. The papermaking slurry is made into paper by sheet forming to obtain a crude insulating paper with a thickness of 0.9 - 1.1 mm; S3. Uniformly coat the crude insulating paper with a silicon-aluminum gel, and then hot roll it with a hot rolling machine at a temperature of 110 - 120 °C to obtain an insulating paper; S4. After coating the epoxy resin adhesive on the insulating paper, wind it uniformly around a flat copper wire, and then perform a heat curing treatment on it to prepare a paper-covered flat copper wire.

2. The preparation method of a paper-covered copper flat wire according to claim 1, wherein In step S1, the dosage ratio of the wood pulp fiber, the pretreated PI fiber and the purified water is 2 g: 1 g: 150 mL; in step S2, the volume ratio of the dissociation slurry to the polysiloxane emulsion is 7: 1; in step S3, the coating amount of the silicon-aluminum gel is 10 g / m 2 ; in step S4, the epoxy resin adhesive is composed of epoxy resin E-42 and 4-aminobutyltriethoxysilane in a weight ratio of 5:

1.

3. The preparation method of a paper-covered copper flat wire according to claim 1, characterized in that, The pretreated PI fibers are processed by the following steps: A1. Mix and stir the polyimide short fibers and the activation liquid, raise the temperature of the reaction system to 50 - 60 °C, keep it warm for 40 - 60 min, and perform post-treatment to obtain activated PI fibers; A2. Mix and stir the activated PI fibers and the acetic acid solution, react at room temperature for 90 - 120 min, and perform post-treatment to obtain the pretreated PI fibers.

4. The preparation method of a paper-covered copper flat wire according to claim 3, characterized in that, In step A1, the solid-liquid ratio of the polyimide short fibers to the activation liquid is 1:10, and the activation liquid is composed of sodium hydroxide, purified water, and N,N-dimethylacetamide in a ratio of 1 g:10 mL:15 mL; in step A2, the solid-liquid ratio of the activated PI fibers to the acetic acid solution is 1:8, and the acetic acid solution is composed of glacial acetic acid and purified water in a ratio of 1 g:5 mL.

5. The preparation method of a paper-covered copper flat wire according to claim 1, characterized in that, The polysiloxane emulsion is processed by the following steps: B1. Mix diethoxysilane-modified DOPO, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methacrylic acid trioxacyclosiloxane to obtain a mixed siloxane solution; B2. Under stirring, drop the mixed siloxane solution into an emulsion at a temperature of 60 - 80 °C. After the dropping is completed, keep it warm for 60 - 80 min, lower the temperature of the reaction system to room temperature, and adjust the pH of the reaction system to 7 to obtain the polysiloxane emulsion.

6. The preparation method of a paper-covered copper flat wire according to claim 5, characterized in that, In step B1, the weight ratio of diethoxysilane-modified DOPO, tetramethyltetravinylcyclotetrasiloxane, octamethylcyclotetrasiloxane, and methacrylic acid trioxacyclosiloxane is 3 - 4:2 - 3:8 - 9:1 - 2; in step B2, the volume ratio of the mixed siloxane solution to the emulsion is 1:20, and the emulsion is composed of anhydrous ethanol, purified water, 80 wt% sulfuric acid, sodium dodecyl sulfate, Tween-80, and polyethylene glycol-400 in a ratio of 30 mL:90 mL:8 mL:1 g:2 g:2 g.

7. The manufacturing method of a paper-covered copper flat wire according to claim 5, characterized in that, The preparation method of diethoxysilane-modified DOPO is as follows: under an inert atmosphere, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide, 3-isocyanatopropylmethyldiethoxysilane and 1,4-dioxane are mixed and stirred, the temperature of the reaction system is raised to 50-60 °C, and the reaction is carried out under insulation for 80-90 min, followed by post-treatment to obtain diethoxysilane-modified DOPO; the dosage ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-methanol-10-oxide to 3-isocyanatopropylmethyldiethoxysilane is 1 mol:1 mol.

8. The preparation method of a paper-covered copper flat wire according to claim 1, characterized in that, The preparation method of the phosphoaluminum gel is as follows: phosphoric acid is heated to 80-90 °C, aluminum hydroxide is added to the phosphoric acid in batches, the reaction is carried out under insulation for 2-3 h, the temperature of the reaction system is cooled to room temperature, 5-hexenyltriethoxysilane and an initiator are added to the reaction system, and the reaction is carried out for 40-60 min to obtain the phosphoaluminum gel.

9. A paper-covered copper flat wire, characterized in that, The paper-covered copper flat wire is prepared by using the preparation method of a paper-covered copper flat wire according to any one of claims 1-8.

10. Application of a paper-covered copper flat wire, characterized in that, The paper-covered copper flat wire prepared by using the preparation method of a paper-covered copper flat wire according to any one of claims 1-8 is applied to a dry-type transformer.

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