Nitrile rubber composition applied to sealed transformer oil and preparation method of nitrile rubber composition

Abstract

The invention discloses a nitrile rubber composition applied to sealed transformer oil and a preparation method thereof, and relates to the technical field of rubber sealing materials, the nitrile rubber composition comprises the following components: 100 parts of raw nitrile rubber and 45-60 parts of modified white carbon black with a two-stage pore structure; 10-14 parts of a plasticizer; 4.5-6.5 parts of a dynamic response vulcanization system; 2.2 to 3.8 parts of a polymerization type anti-aging agent; 4.8 to 5.5 parts of zinc oxide; and 1.0 to 1.3 parts of stearic acid. According to the invention, mercaptopropyl modified nano silicon dioxide is loaded in a mesoporous region through two-stage pore structure modified white carbon black to reinforce the filler-matrix interface bonding force, and a perfluorosilane grafted lauric acid / silicon dioxide composite phase change material is encapsulated in a macroporous region; ferroferric oxide-benzoxazine resin in a dynamic response vulcanization system induced by an alternating electric field is directionally arranged to form a three-dimensional enhanced network, and the service life is prolonged to 3 times of that of a conventional product by combining a pulse air pressure gradient vulcanization process; and under the synergistic effect of supercritical CO2 hole sealing and electric field assisted thin-passing, interface stress cracking is thoroughly eliminated, and the dispersion uniformity of the filler is improved by 40%.

Description

Technical Field

[0001] This invention relates to the field of rubber sealing materials technology, specifically to a nitrile rubber composition for sealing transformer oil and its preparation method. Background Technology

[0002] Transformer oil sealing systems are exposed to high-temperature oil immersion environments for extended periods and must withstand transient temperature rises caused by sudden load changes. Traditional nitrile rubber seals are prone to permanent compression deformation and deterioration due to plasticizer migration and insufficient thermal stability of cross-linked networks, leading to pressure attenuation at the sealing interface and subsequent leakage.

[0003] Current technologies mainly improve oil resistance by increasing acrylonitrile content or adding inorganic fillers, but they cannot reconcile the contradiction between swelling inhibition and resistance to transient thermal expansion. Although temperature control methods for phase change materials have been introduced, conventional single-pore carriers have low loading rates and weak interfacial bonding, and the leakage of phase change components at high temperatures will accelerate rubber aging.

[0004] The existing system has three limitations: traditional vulcanized networks lack temperature responsiveness and are difficult to adapt to dynamic thermal stress; physical blending of phase change materials leads to a decrease in the stability of the sealing interface; and defects at the filler-matrix interface exacerbate the risk of stress cracking in hot oil environments, resulting in a sealing life far below the design life of the transformer. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a nitrile rubber composition for use in sealing transformer oil and its preparation method, in order to solve the technical problems of traditional vulcanized networks lacking temperature responsiveness and being unable to adapt to dynamic thermal stress; physical blending of phase change materials leading to decreased stability of the sealing interface; and filler-matrix interface defects exacerbating the risk of stress cracking in hot oil environments, resulting in a sealing life far below the design life of the transformer.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a nitrile rubber composition for use in sealing transformer oil and its preparation method.

[0007] A first aspect of the present invention provides a nitrile rubber composition for use in sealing transformer oil, comprising the following components in parts by weight:

[0008] 100 parts of nitrile rubber raw material, with an acrylonitrile content of 33-37 wt%;

[0009] 45-60 parts of bipolar pore structure modified silica, in which modified nano-silica particles are loaded in the mesoporous region (pore size 2-8nm) and composite phase change material is encapsulated in the macroporous region (pore size 20-50nm), the phase change material accounting for 28-36% of the total weight of silica.

[0010] The plasticizer, 10-14 parts, is a compound composed of polyester plasticizer and epoxidized soybean oil in a mass ratio of 1.2:1 to 1:1;

[0011] The dynamic response vulcanization system comprises 4.5-6.5 parts of peroxide crosslinking agent (3.0-3.8 parts), long-chain alkyl-substituted benzoxazine resin (1.3-1.8 parts, alkyl carbon atoms 10-14), and pentaerythritol tetraacrylate (0.4-0.9 parts), wherein the resin has iron oxide nanoparticles with a particle size of 8-12 nm (accounting for 5-10% of the resin weight) bonded to the oxygen heterocycle.

[0012] Polymer-type antioxidant 2.2-3.8 parts, zinc oxide 4.2-4.8 parts, stearic acid 1.0-1.3 parts;

[0013] The composite phase change material is a composite of lauric acid and nano-silica (mass ratio 6.5:1 to 7.5:1), and the surface of the nano-silica is grafted with perfluorooctyltriethoxysilane (grafting density 1.2-2.5 groups per square nanometer).

[0014] A second aspect of the present invention provides a method for preparing the above-described composition, comprising the following steps:

[0015] S1. Vacuum impregnation modification: Dimorphic silica was injected into molten composite phase change material under vacuum of -0.095 MPa and 75°C, and stirred under pressure for 2 hours.

[0016] S2. Low-temperature initial mixing: Nitrile rubber raw material, stearic acid and 1 / 3 plasticizer are mixed at 50±2℃ for 3 minutes;

[0017] S3. Filler dispersion: Add modified silica, antioxidant and remaining plasticizer, and mix at 85-95℃ for 6 minutes;

[0018] S4. Electric field assisted vulcanization: Cool down to below 35℃, add dynamic response vulcanization system and zinc oxide, mix and then pass through an alternating electric field (field strength 0.8-1.2kV / mm, frequency 1-5Hz) 8 times. The direction of the electric field is at a 45° angle to the axis of the roller and the direction is reversed every 2 passes.

[0019] S5. Gradient curing: The rubber compound is successively cured at 155℃ for 4 minutes, 165℃ for 12 minutes (applying 0.5-1.0MPa pulse air pressure, frequency 2Hz), and 170℃ for 5 minutes.

[0020] Preferably, after step S1, a supercritical CO2-assisted sealing treatment (pressure 12-15 MPa, temperature 45°C) is further included to form a 50-100 nm silica deposition layer to seal the pores.

[0021] In summary, the present invention has the following main beneficial effects:

[0022] This invention strengthens the filler-matrix interface bonding by loading mercaptopropyl-modified nano-silica onto bipolar pore-structured modified silica in the mesoporous region, while simultaneously encapsulating perfluorosilane-grafted lauric acid / silica composite phase change material (with a loading rate as high as 36%) in the macroporous region. In a synergistic alternating electric field-induced dynamic response vulcanization system, ferric oxide-benzoxazine resin forms a directionally arranged three-dimensional reinforcing network. Combined with a pulsed gas pressure gradient vulcanization process, this invention achieves three major breakthroughs: stable control of interfacial pressure fluctuations within 5% under a 120℃ transient temperature rise with zero phase change material leakage; reduced compression set to below 28.5% after 150℃×1000h hot oil aging, extending lifespan to three times that of conventional products; and the synergistic effect of supercritical CO2 sealing and electric field-assisted thin-walling completely eliminates interfacial stress cracking, improving filler dispersion uniformity by 40%. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the dual-hole structure of the present invention;

[0024] Figure 2 This is a flowchart illustrating the overall process flow of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] The embodiments of the present invention will now be described.

[0027] Example 1

[0028] 1. Raw material ratio (by weight)

[0029] Nitrile rubber raw material (acrylonitrile content 35wt%): 100 parts;

[0030] Bipolar porous modified silica: 52 parts;

[0031] Mesoporous region: pore size 5nm, loaded with mercaptopropyl modified nano-SiO2 (particle size 20nm, loading 15%);

[0032] Large pore region: pore size 35nm, encapsulated composite phase change material (lauric acid: nano SiO2 = 7:1, phase change material accounts for 32%);

[0033] Sealing layer: 80nm SiO2 deposition layer formed by supercritical CO2 treatment;

[0034] Plasticizer: 12 parts (polyester plasticizer: epoxidized soybean oil = 1.1:1);

[0035] Dynamic response vulcanization system: 5.5 parts;

[0036] 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane: 3.4 parts;

[0037] C12 alkylbenzoxazin resin (bonded with 10nm Fe3O4, accounting for 8%): 1.6 parts;

[0038] Pentaerythritol tetraacrylate: 0.5 parts;

[0039] Polymerized antioxidant (NAPM / TMQ = 1:1): 3.0 parts;

[0040] Zinc oxide: 4.5 parts;

[0041] Stearic acid: 1.2 parts.

[0042] 2. Preparation process

[0043] S1. Vacuum impregnation + sealing: Silica is impregnated with molten phase change material at -0.095MPa / 75℃, followed by supercritical CO2 treatment (13MPa / 45℃).

[0044] S2, Low-temperature initial mixing: Nitrile rubber + stearic acid + 4 parts plasticizer, mix at 50℃ for 3 minutes.

[0045] S3. Filler dispersion: Add modified silica, antioxidant, and remaining plasticizer, and mix at 90℃ for 6 minutes.

[0046] S4. Electric field sulfidation: Add sulfidation system + zinc oxide at 35℃, and pass through a 1.0kV / mm alternating electric field (3Hz) 8 times (reversing direction every 2 times).

[0047] S5, Gradient curing: 155℃×4min→165℃×12min(0.8MPa pulse air pressure)→170℃×5min.

[0048] 3. Performance Data

[0049]

[0050]

[0051] Example 2:

[0052] 1. Raw material ratio (parts by weight)

[0053] Nitrile rubber (acrylonitrile 33wt%): 100 parts

[0054] Bipolar pore silica: 45 parts

[0055] Mesoporous region: pore size 2nm, loaded with modified SiO2 (12% loading).

[0056] Macroporous region: pore size 20nm, phase change material (lauric acid:SiO2 = 6.5:1, accounting for 28%)

[0057] Sealing layer: 50nm SiO2 deposition layer

[0058] Plasticizer: 10 parts (polyester: epoxidized soybean oil = 1.2:1)

[0059] Vulcanization system: 4.5 parts (3.0 parts peroxide + 1.3 parts C10 benzoxazin + 0.4 parts pentaerythritol ester)

[0060] Other components are added to the minimum extent permitted by claim.

[0061] 2. Key process parameters

[0062] Electric field strength: 0.8 kV / mm

[0063] Pulse pressure: 0.5MPa

[0064] 3. Performance Data

[0065]

[0066]

[0067] Example 3:

[0068] 1. Raw material ratio (parts by weight)

[0069] Nitrile rubber (acrylonitrile 37wt%): 100 parts

[0070] Bipolar pore silica: 60 parts

[0071] Mesoporous region: pore size 8 nm, loaded with modified SiO2 (18% loading).

[0072] Macroporous region: pore size 50nm, phase change material (lauric acid:SiO2 = 7.5:1, accounting for 36%)

[0073] Sealing layer: 100nm SiO2 deposition layer

[0074] Plasticizer: 14 parts (polyester: epoxidized soybean oil = 1:1)

[0075] Vulcanization system: 6.5 parts (3.8 parts peroxide + 1.8 parts C14 benzoxazin + 0.9 parts pentaerythritol ester)

[0076] 2. Key process parameters

[0077] Electric field strength: 1.2 kV / mm

[0078] Pulse pressure: 1.0 MPa

[0079] 3. Performance Data

[0080] Test Project numerical values Sealing pressure fluctuation rate 3.9％ Compression set at 150℃ for 1000 hours 25.3％ Phase change material permeation rate 0％ Tensile strength retention 91.2％ Interface Defect Count <![CDATA[1.0 / μm 2 ]]>

[0081] Comparative Example 1:

[0082] Formula: Same as Example 1, but the silica is replaced with ordinary silica + physically mixed phase change material. Process: Supercritical sealing and electric field sulfidation are omitted.

[0083] Performance: Sealing pressure fluctuation rate: 23.7%

[0084] Compression set: 64.8%

[0085] Phase change material exudation rate: 9.2% (150℃×200h)

[0086] Comparative Example 2:

[0087] Formula: Same as Example 1

[0088] Process: Elimination of alternating electric field, conventional thin-walled circuit

[0089] Performance: Filler dispersion uniformity: 4.3 defects / μm 2

[0090] Crack length after aging in hot oil at 150℃: 280μm

[0091] Sealing life: 7 years

[0092] Comparative Example 3

[0093] Formula: Eliminate dynamic response vulcanization system

[0094] Performance of the modified formula: 2.5 parts sulfur + 1.5 parts accelerator CZ + 0.5 parts TT

[0095] Test data numerical values 120℃ sealing pressure fluctuation rate 31.5％ Thermal decomposition onset temperature 268℃ Permanent deformation increment after transient temperature rise 18.7％

[0096] Overall performance comparison table:

[0097]

[0098]

[0099] Note: Comparative Example 1 showed exudation after 200 hours.

[0100] Effect Mechanism Analysis

[0101] Synergistic effect of bi-level holes

[0102] The mesoporous nano-SiO2 improves the bonding strength between the filler and rubber interface, with an interfacial peel strength of 8.3 MPa (compared to 5.1 MPa for ordinary fillers).

[0103] The macroporous phase change material has an endothermic value of 186 J / g and a temperature control response time of less than 15 seconds.

[0104] Directional effect of electric field sulfidation

[0105] Fe3O4-benzoxazine forms a 45° cross-linked network under an electric field (orientation degree of 0.82 as shown by wide-angle X-ray).

[0106] Improved temperature stability of dynamic modulus of vulcanizate: fluctuation <12% from -40℃ to 150℃.

[0107] Advantages of gradient curing

[0108] Pulsed air pressure affects bubble size distribution:

[0109] Bubble diameter <10μm proportion Example 1 98.7％ Conventional vulcanization 73.5％

[0110] The sealing pressure fluctuation rate (3.9-4.8%) of Examples 1-3 was reduced by more than 80% compared with Comparative Example 1 (23.7%), proving that the synergistic effect of the bi-hole structure encapsulation phase change material (loading rate 28-36%) and the dynamic response vulcanization system (directional crosslinking of iron oxide) can effectively suppress transient temperature rise shock.

[0111] The compression set (25.3-28.1%) of the example after hot oil aging at 150℃ for 1000h was only 40% of that of Comparative Example 1 (64.8%), and the phase change material exudation rate remained at 0% (Comparative Example 1 exuded 9.2% after 200h). This, combined with supercritical CO2 sealing (sealing layer 50-100nm) and electric field-assisted vulcanization (defect number 1.0-1.5 / μm), demonstrates superior performance. 2 This enables the sealing life to exceed 15 years, which is 3 times that of traditional products (4-5 years);

[0112] Data on filler dispersion uniformity showed that the number of interface defects in Example 2 was 4.3 / μm compared to Comparative Example 2. 2 The risk of thermal stress cracking was reduced by more than 70%, confirming that the 45° alternating electric field thin pass and pulsed air pressure gradient curing can completely eliminate the risk of thermal stress cracking.

[0113] This invention achieves simultaneous breakthroughs in dynamic thermal stability (fluctuation rate <5%), long-term sealing performance (compression deformation <28.5%), and interface integrity (zero leakage + low defects) in the field of transformer oil sealing through a triple synergistic innovation of "dual-level hole encapsulation - dynamic vulcanization - gradient curing". It solves the core pain point that traditional technologies cannot coordinate the contradiction between swelling inhibition and thermal expansion resistance.

[0114] Although embodiments of the present invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions, and variations to the embodiments as needed without departing from the principles and spirit of the invention, but such modifications, substitutions, and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A nitrile rubber composition for use in sealing transformer oil, characterized in that: It contains the following components by weight: 100 parts of nitrile rubber raw material, wherein the acrylonitrile content of the nitrile rubber raw material is 33-37 wt%; 45-60 parts of bipolar porous modified silica; 10-14 parts of plasticizer, wherein the plasticizer is a compound composed of polyester plasticizer and epoxidized soybean oil in a mass ratio of 1.2:1 to 1:1; Dynamic response vulcanization system: 4.5-6.5 parts; Polymer-type antioxidant: 2.2-3.8 parts; Zinc oxide 4.2-4.8 parts; Stearic acid 1.0-1.3 parts; The bipolar pore structure modified silica comprises mesoporous regions and macroporous regions. The mesoporous regions have a pore size of 2-8 nm and are loaded with modified nano-silica particles. The macroporous regions have a pore size of 20-50 nm and are encapsulated with composite phase change materials. The composite phase change materials account for 28-36% of the total weight of the bipolar pore structure modified silica.

2. The nitrile rubber composition for sealing transformer oil according to claim 1, characterized in that: The dynamic response vulcanization system is composed of a peroxide crosslinking agent, a long-chain alkyl-substituted benzoxazine resin, and pentaerythritol tetraacrylate. The amount of the peroxide crosslinking agent is 3.0-3.8 parts; The amount of the long-chain alkyl-substituted benzoxazine resin is 1.3-1.8 parts, and the number of carbon atoms of its alkyl substituent is 10-14. The amount of pentaerythritol tetraacrylate used is 0.4-0.9 parts; The long-chain alkyl-substituted benzoxazine resin has iron oxide nanoparticles bonded to its heterocyclic rings. The iron oxide nanoparticles have a particle size of 8-12 nm and account for 5-10% of the weight of the long-chain alkyl-substituted benzoxazine resin.

3. The nitrile rubber composition for sealing transformer oil according to claim 2, characterized in that: The peroxide crosslinking agent is 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, which has a half-life of not less than 10 minutes at 150°C.

4. The nitrile rubber composition for sealing transformer oil according to claim 1, characterized in that: The composite phase change material is a composite of lauric acid and nano-silica, with a mass ratio of lauric acid to nano-silica of 6.5:1 to 7.5:

1. The surface of the nano-silica is grafted with perfluorooctyltriethoxysilane at a grafting density of 1.2-2.5 groups per square nanometer.

5. A method for preparing the composition according to any one of claims 1-4, characterized in that: Includes the following steps: S1. Vacuum impregnation modification: Place bipolar porous silica in a vacuum reactor, inject molten composite phase change material under vacuum of -0.095MPa and temperature of 75℃, and maintain pressure and stir for 2 hours. S2, Low-temperature initial mixing: Add nitrile rubber raw rubber, stearic acid and plasticizer accounting for 1 / 3 of the total amount of plasticizer to the internal mixer and mix at 50±2℃ for 3 minutes; S3. Filler dispersion: Add modified silica, antioxidant and remaining plasticizer to the product of step S2, and mix at 85-95℃ for 6 minutes. S4. Electric field assisted vulcanization: The product from step S3 is cooled to below 35°C, and a dynamic response vulcanization system and zinc oxide are added. After mixing, the mixture is transferred to a two-roll mill and passed through a vertical alternating electric field 8 times. The electric field strength of the alternating electric field is 0.8-1.2kV / mm and the frequency is 1-5Hz. S5. Gradient curing: The thin-passed rubber compound is vulcanized. The vulcanization process is 155℃ for 4 minutes, 165℃ for 12 minutes, and 170℃ for 5 minutes.

6. The preparation method according to claim 5, characterized in that: After vacuum impregnation in step S1, supercritical CO2-assisted sealing treatment is performed at a pressure of 12-15 MPa and a temperature of 45°C, so that a silica deposition layer with a thickness of 50-100 nm is formed at the pore opening.

7. The preparation method according to claim 5, characterized in that: In step S4, the direction of the alternating electric field is at a 45° angle to the axis of the open mill roller, and the direction of the electric field is reversed after every two passes.

8. The preparation method according to claim 5, characterized in that: In step S5, during the gradient curing process, a pulsed air pressure is applied to the vulcanization mold at the 165°C stage. The pressure of the pulsed air pressure is 0.5-1.0 MPa, and the pulse frequency is 2 Hz.

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