An epoxy encapsulant for sensors and its preparation method

Abstract

This invention relates to the field of epoxy encapsulant technology, and discloses an epoxy encapsulant for sensors and its preparation method. The method includes premixing epoxy resin base material, primary dispersion, secondary mixing, final mixing and degassing, filtration and packaging. Through the synergistic combination of bisphenol A type epoxy resin and phenolic epoxy resin, and the ring-opening reaction with an acid anhydride curing agent, a dense three-dimensional cross-linked network structure is formed, which closes the pores between molecular chains and blocks charge migration paths, thereby improving the electrical insulation performance of the epoxy encapsulant. At the same time, the introduction of polysulfide rubber toughening agent enhances the flexibility and impact resistance of the colloid, improving the reliability of the encapsulation. By using plasma treatment and silane coupling agent surface modification of nano-alumina, the insulation effect is strengthened and the overall mechanical strength of the encapsulant is improved.

Description

Technical Field

[0001] This invention relates to the field of epoxy encapsulant technology, specifically to an epoxy encapsulant for sensors and its preparation method. Background Technology

[0002] Epoxy encapsulants are available in two types: single-component and two-component. Compared to two-component epoxy encapsulants, single-component epoxy encapsulants offer superior performance in terms of convenience, temperature resistance, and adhesion, and are widely used in packaging processes for integrated circuits, electronic components, and other electronic components.

[0003] Currently, because epoxy encapsulants for sensors need to balance storage stability and curing activity in a single-component system, the dispersion uniformity of nanofillers and their interfacial bonding with the resin matrix are often insufficient in conventional processes. This can easily lead to microscopic defects in the cured encapsulation layer. If there is local electric field concentration or environmental moisture penetration, it may result in a decrease in insulation reliability, making it difficult to meet the encapsulation requirements for long-term stability of high-precision sensors.

[0004] Therefore, an epoxy encapsulating adhesive for sensors and its preparation method are proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an epoxy encapsulating adhesive for sensors and its preparation method, which solves the problem mentioned in the background art of decreased insulation reliability and difficulty in meeting the packaging requirements for long-term stability of high-precision sensors.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an epoxy encapsulating adhesive for sensors, made from raw materials comprising the following parts by weight:

[0007] 40-60 parts of bisphenol A type epoxy resin, 20-30 parts of phenolic epoxy resin, 25-35 parts of acid anhydride curing agent, 0.5-2 parts of latent curing accelerator, 15-25 parts of nano alumina surface-treated with silane coupling agent, 1-3 parts of hydrogenated castor oil derivative thixotropic agent, 2-5 parts of γ-glycidyl etheroxypropyltrimethoxysilane, and 3-8 parts of polysulfide rubber toughening agent.

[0008] The nano-alumina has a particle size of 20-50 nm, and its surface treatment process includes:

[0009] Nano-alumina is placed in a plasma treatment device and treated with 200-400W power for 10-30 minutes under an argon atmosphere. Then it is immediately immersed in an ethanol solution of 5wt% γ-glycidoxypropyltrimethoxysilane and stirred at 60-70℃ for 2-4 hours. After filtration, washing and drying, it is obtained.

[0010] Preferably, the bisphenol A type epoxy resin has an epoxy equivalent of 180-200 g / eq, and the phenolic epoxy resin has an epoxy equivalent of 160-180 g / eq.

[0011] Preferably, the anhydride curing agent is one or more combinations of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, or hexahydrophthalic anhydride.

[0012] Preferably, the latent curing accelerator is a microencapsulated product of 2-methylimidazole, 2-phenylimidazole or 2-ethyl-4-methylimidazole, and the wall material of the microcapsule is polyurethane, with a core material content of 60-80 wt%.

[0013] Preferably, the polysulfide rubber toughening agent has a molecular weight of 3000-6000 and a mercaptan content of 2-5 wt%.

[0014] A method for preparing an epoxy encapsulating adhesive for sensors includes the following steps:

[0015] Step 1: Premix epoxy resin base material. Add bisphenol A type epoxy resin and phenolic epoxy resin to a planetary stirring kettle with a heating jacket and vacuum system. Heat to 70-80℃ and stir at 100-200 rpm for 20-40 minutes until the mixture is uniform.

[0016] Step 2: Dispersion at one time. The surface-treated nano-alumina is slowly added to the epoxy resin base material obtained in Step 1 under vacuum. During the addition process, the temperature inside the vessel is maintained at 70-80℃ and the vacuum degree is not lower than -0.095MPa. After the addition is completed, the stirring speed is increased to 400-600rpm and stirring is continued for 60-90 minutes.

[0017] Step 3: Secondary mixing. Cool the mixture obtained in Step 2 to 40-50℃, and add the acid anhydride curing agent, hydrogenated castor oil derivative thixotropic agent, γ-glycidyl etheroxypropyltrimethoxysilane and polysulfide rubber toughening agent in sequence. Stir at 200-300 rpm for 30-45 minutes.

[0018] Step 4: Final mixing and degassing. Add the latent curing accelerator to the mixture obtained in Step 3, stir at 100-200 rpm for 15-25 minutes, then turn on the vacuum system to maintain the vacuum degree in the reactor below -0.098 MPa, and stir at low speed at 40-50℃ for 60-120 minutes to degas, so as to obtain a uniform epoxy encapsulating colloid.

[0019] Step 5: Filtration and packaging. The colloid after degassing in step 4 is filtered under pressure through a 200-300 mesh filter and then packaged under anhydrous and oxygen-free conditions.

[0020] Preferably, the nano-alumina in step two is added at a uniform rate over 20-30 minutes using a screw feeder.

[0021] Preferably, the defoaming process in step four is divided into two stages:

[0022] In the first stage, degassing is performed at a vacuum of -0.095MPa to -0.098MPa for 30-60 minutes. In the second stage, the rotation speed is reduced to 50-100rpm, and degassing continues for another 30-60 minutes.

[0023] Preferably, the pressure of the pressurized filtration in step five is 0.2-0.4 MPa, and the relative humidity of the filtration environment is controlled below 10% by a dehumidification system;

[0024] The filter used is a 300-mesh double-layer stainless steel sintered mesh. The filtration process is carried out in a closed, insulated pipe, with the pipe temperature maintained at 45-55℃.

[0025] Preferably, the planetary mixer has a double-frame impeller with a revolution speed of 10-30 rpm and a rotation speed of 100-600 rpm.

[0026] The jacket of the stirred tank uses hot oil as the heat transfer medium, and the temperature control accuracy is ±1℃.

[0027] A condenser is installed between the vacuum system and the stirred tank to capture the extracted volatile substances.

[0028] Compared with the prior art, the present invention provides an epoxy encapsulating adhesive for sensors and its preparation method, which has the following beneficial effects:

[0029] 1. In this invention, the synergistic combination of bisphenol A type epoxy resin and phenolic epoxy resin, and the ring-opening reaction with acid anhydride curing agent, forms a dense three-dimensional cross-linked network structure, which closes the pores between molecular chains and blocks the charge migration path, thereby improving the electrical insulation performance of the epoxy encapsulant. At the same time, the introduction of polysulfide rubber toughening agent enhances the flexibility and impact resistance of the colloid, and improves the reliability of the encapsulation.

[0030] 2. In this invention, nano-alumina with plasma treatment and silane coupling agent surface modification is used to enhance its surface activity, form a stronger interfacial bond with the epoxy resin matrix, reduce microcracks and voids at the interface, avoid the risk of breakdown caused by local electric field concentration, strengthen the insulation effect, and improve the overall mechanical strength of the encapsulating adhesive.

[0031] 3. In this invention, through vacuum degassing and pressure filtration steps, air bubbles and impurities in the colloid are removed under strictly controlled temperature and humidity conditions, ensuring the uniformity and density of the colloid. Combined with the microencapsulation technology of latent curing accelerator, the curing process is made stable and controllable, improving the bonding strength and long-term stability of the encapsulating adhesive. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: An epoxy encapsulating compound for sensors, made from raw materials comprising the following parts by weight:

[0034] 40 parts of bisphenol A type epoxy resin, 20 parts of phenolic epoxy resin, 25 parts of acid anhydride curing agent, 0.5 parts of latent curing accelerator, 15 parts of nano alumina surface treated with silane coupling agent, 1 part of hydrogenated castor oil derivative thixotropic agent, 2 parts of γ-glycidyl etheroxypropyltrimethoxysilane, and 3 parts of polysulfide rubber toughening agent.

[0035] The nano-alumina has a particle size of 20 nm, and its surface treatment process includes:

[0036] Nano-alumina was placed in a plasma treatment device and treated at 200W power for 10 minutes under an argon atmosphere. Then it was immediately immersed in an ethanol solution of 5wt% γ-glycidoxypropyltrimethoxysilane and stirred at 60°C for 2 hours. After filtration, washing and drying, it was obtained.

[0037] The epoxy equivalent of bisphenol A type epoxy resin is 180 g / eq, and the epoxy equivalent of phenolic epoxy resin is 160 g / eq.

[0038] The anhydride curing agent is one or more combinations of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, or hexahydrophthalic anhydride.

[0039] The latent curing accelerator is a microencapsulated product of 2-methylimidazole, 2-phenylimidazole or 2-ethyl-4-methylimidazole, the wall material of the microcapsule is polyurethane, and the core material content is 60wt%.

[0040] The polysulfide rubber toughening agent has a molecular weight of 3000 and a mercaptan content of 2wt%.

[0041] A method for preparing an epoxy encapsulating adhesive for sensors includes the following steps:

[0042] Step 1: Premix epoxy resin base material. Add bisphenol A type epoxy resin and phenolic epoxy resin to a planetary stirring vessel equipped with a heating jacket and vacuum system. Heat to 70°C and stir at 100 rpm for 20 minutes until the mixture is uniform.

[0043] Step 2: Dispersion: The surface-treated nano-alumina is slowly added to the epoxy resin base material obtained in Step 1 under vacuum. During the addition process, the temperature inside the vessel is maintained at 70℃ and the vacuum degree is not lower than -0.095MPa. After the addition is completed, the stirring speed is increased to 400rpm and stirring is continued for 60 minutes.

[0044] Step 3: Secondary mixing. Cool the mixture obtained in Step 2 to 40°C, and add the acid anhydride curing agent, hydrogenated castor oil derivative thixotropic agent, γ-glycidyl etheroxypropyltrimethoxysilane and polysulfide rubber toughening agent in sequence. Stir at 200 rpm for 30 minutes.

[0045] Step 4: Final mixing and degassing. Add the latent curing accelerator to the mixture obtained in Step 3, stir at 100 rpm for 15 minutes, then turn on the vacuum system to maintain the vacuum degree in the reactor below -0.098 MPa, and stir at low speed at 40°C for 60 minutes to degas, so as to obtain a uniform epoxy encapsulating colloid.

[0046] Step 5: Filtration and packaging. The colloid after degassing in Step 4 is filtered under pressure through a 200-mesh filter and then packaged under anhydrous and oxygen-free conditions.

[0047] In step two, the nano-alumina is added at a constant speed over 20 minutes using a screw feeder.

[0048] Step four, the defoaming process, is divided into two stages:

[0049] In the first stage, degassing was performed for 30 minutes under a vacuum of -0.095 MPa. In the second stage, the rotation speed was reduced to 50 rpm, and degassing continued for another 30 minutes.

[0050] In step five, the pressure for pressurized filtration is 0.2 MPa, and the relative humidity of the filtration environment is controlled below 10% by a dehumidification system.

[0051] The filter used is a 300-mesh double-layer stainless steel sintered mesh. The filtration process is carried out in a closed, insulated pipe, and the pipe temperature is maintained at 45℃.

[0052] The planetary mixer has a double-frame impeller with a revolution speed of 10 rpm and a rotation speed of 100 rpm.

[0053] The jacket of the stirred tank uses hot oil as the heat transfer medium, and the temperature control accuracy is ±1℃.

[0054] A condenser is installed between the vacuum system and the stirred tank to capture the extracted volatile substances.

[0055] Example 2: An epoxy encapsulating compound for sensors, made from raw materials comprising the following parts by weight:

[0056] 50 parts of bisphenol A type epoxy resin, 25 parts of phenolic epoxy resin, 30 parts of acid anhydride curing agent, 1.2 parts of latent curing accelerator, 20 parts of nano alumina surface treated with silane coupling agent, 2 parts of hydrogenated castor oil derivative thixotropic agent, 3 parts of γ-glycidyl etheroxypropyltrimethoxysilane, and 5 parts of polysulfide rubber toughening agent.

[0057] The nano-alumina has a particle size of 35 nm, and its surface treatment process includes:

[0058] Nano-alumina was placed in a plasma treatment device and treated at 300W power for 20 minutes under an argon atmosphere. Then it was immediately immersed in an ethanol solution of 5wt% γ-glycidyl oxypropyltrimethoxysilane and stirred at 65°C for 3 hours. After filtration, washing and drying, it was obtained.

[0059] The epoxy equivalent of bisphenol A type epoxy resin is 190 g / eq, and the epoxy equivalent of phenolic epoxy resin is 170 g / eq.

[0060] The anhydride curing agent is one or more combinations of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, or hexahydrophthalic anhydride.

[0061] The latent curing accelerator is a microencapsulated product of 2-methylimidazole, 2-phenylimidazole or 2-ethyl-4-methylimidazole, the wall material of the microcapsule is polyurethane, and the core material content is 70 wt%.

[0062] The polysulfide rubber toughening agent has a molecular weight of 4500 and a mercaptan content of 3.5 wt%.

[0063] A method for preparing an epoxy encapsulating adhesive for sensors includes the following steps:

[0064] Step 1: Premix epoxy resin base material. Add bisphenol A type epoxy resin and phenolic epoxy resin to a planetary stirring vessel equipped with a heating jacket and vacuum system. Heat to 75°C and stir at 150 rpm for 30 minutes until the mixture is uniform.

[0065] Step 2: First dispersion. The surface-treated nano-alumina is slowly added to the epoxy resin base material obtained in Step 1 under vacuum. During the addition process, the temperature inside the vessel is maintained at 75℃ and the vacuum degree is not lower than -0.095MPa. After the addition is completed, the stirring speed is increased to 500rpm and stirring is continued for 75 minutes.

[0066] Step 3: Secondary mixing. Cool the mixture obtained in Step 2 to 45°C, and add the acid anhydride curing agent, hydrogenated castor oil derivative thixotropic agent, γ-glycidyl etheroxypropyltrimethoxysilane and polysulfide rubber toughening agent in sequence. Stir at 250 rpm for 37 minutes.

[0067] Step 4: Final mixing and degassing. Add the latent curing accelerator to the mixture obtained in Step 3, stir at 150 rpm for 20 minutes, then turn on the vacuum system to maintain the vacuum degree in the reactor below -0.098 MPa, and stir at low speed at 45°C for 90 minutes to degas, so as to obtain a uniform epoxy encapsulating colloid.

[0068] Step 5: Filtration and packaging. The colloid after degassing in step 4 is filtered under pressure through a 250-mesh filter and then packaged under anhydrous and oxygen-free conditions.

[0069] In step two, the nano-alumina is added at a constant speed over 25 minutes using a screw feeder.

[0070] Step four, the defoaming process, is divided into two stages:

[0071] In the first stage, degassing was performed for 45 minutes under a vacuum of -0.096 MPa. In the second stage, the rotation speed was reduced to 75 rpm, and degassing continued for another 45 minutes.

[0072] In step five, the pressure for pressurized filtration is 0.3 MPa, and the relative humidity of the filtration environment is controlled below 10% by a dehumidification system.

[0073] The filter used is a 300-mesh double-layer stainless steel sintered mesh. The filtration process is carried out in a closed, insulated pipe, and the pipe temperature is maintained at 50℃.

[0074] The planetary mixer has a double-frame impeller with a revolution speed of 20 rpm and a rotation speed of 350 rpm.

[0075] The jacket of the stirred tank uses hot oil as the heat transfer medium, and the temperature control accuracy is ±1℃.

[0076] A condenser is installed between the vacuum system and the stirred tank to capture the extracted volatile substances.

[0077] Example 3: An epoxy encapsulating compound for sensors, made from raw materials comprising the following parts by weight:

[0078] 60 parts of bisphenol A type epoxy resin, 30 parts of phenolic epoxy resin, 35 parts of acid anhydride curing agent, 2 parts of latent curing accelerator, 25 parts of nano alumina surface treated with silane coupling agent, 3 parts of hydrogenated castor oil derivative thixotropic agent, 5 parts of γ-glycidyl etheroxypropyltrimethoxysilane, and 8 parts of polysulfide rubber toughening agent.

[0079] The nano-alumina has a particle size of 50 nm, and its surface treatment process includes:

[0080] Nano-alumina was placed in a plasma treatment device and treated at 400W power for 30 minutes under an argon atmosphere. Then it was immediately immersed in an ethanol solution of 5wt% γ-glycidoxypropyltrimethoxysilane and stirred at 70°C for 4 hours. After filtration, washing and drying, it was obtained.

[0081] The epoxy equivalent of bisphenol A type epoxy resin is 200 g / eq, and the epoxy equivalent of phenolic epoxy resin is 180 g / eq.

[0082] The anhydride curing agent is one or more combinations of methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, or hexahydrophthalic anhydride.

[0083] The latent curing accelerator is a microencapsulated product of 2-methylimidazole, 2-phenylimidazole or 2-ethyl-4-methylimidazole, the wall material of the microcapsule is polyurethane, and the core material content is 80 wt%.

[0084] The polysulfide rubber toughening agent has a molecular weight of 6000 and a mercaptan content of 5wt%.

[0085] A method for preparing an epoxy encapsulating adhesive for sensors includes the following steps:

[0086] Step 1: Premix epoxy resin base material. Add bisphenol A type epoxy resin and phenolic epoxy resin to a planetary stirring vessel equipped with a heating jacket and vacuum system. Heat to 80°C and stir at 200 rpm for 40 minutes until the mixture is uniform.

[0087] Step 2: Dispersion: The surface-treated nano-alumina is slowly added to the epoxy resin base material obtained in Step 1 under vacuum. During the addition process, the temperature inside the vessel is maintained at 80℃ and the vacuum degree is not lower than -0.095MPa. After the addition is completed, the stirring speed is increased to 600rpm and stirring is continued for 90 minutes.

[0088] Step 3: Secondary mixing. Cool the mixture obtained in Step 2 to 50°C, and add the acid anhydride curing agent, hydrogenated castor oil derivative thixotropic agent, γ-glycidyl etheroxypropyltrimethoxysilane and polysulfide rubber toughening agent in sequence. Stir at 300 rpm for 45 minutes.

[0089] Step 4: Final mixing and degassing. Add the latent curing accelerator to the mixture obtained in Step 3, stir at 200 rpm for 25 minutes, then turn on the vacuum system to maintain the vacuum degree in the reactor below -0.098 MPa, and stir at low speed at 50°C for 120 minutes to degas, so as to obtain a uniform epoxy encapsulating colloid.

[0090] Step 5: Filtration and packaging. The colloid after degassing in Step 4 is filtered under pressure through a 300-mesh filter and then packaged under anhydrous and oxygen-free conditions.

[0091] In step two, the nano-alumina is added at a uniform rate over 30 minutes using a screw feeder.

[0092] Step four, the defoaming process, is divided into two stages:

[0093] In the first stage, degassing was performed for 60 minutes under a vacuum of -0.098 MPa. In the second stage, the rotation speed was reduced to 100 rpm, and degassing continued for another 60 minutes.

[0094] In step five, the pressure for pressurized filtration is 0.4 MPa, and the relative humidity of the filtration environment is controlled below 10% by a dehumidification system.

[0095] The filter used is a 300-mesh double-layer stainless steel sintered mesh. The filtration process is carried out in a closed, insulated pipe, and the pipe temperature is maintained at 55℃.

[0096] The planetary mixer has a double-frame impeller with a revolution speed of 30 rpm and a rotation speed of 600 rpm.

[0097] The jacket of the stirred tank uses hot oil as the heat transfer medium, and the temperature control accuracy is ±1℃.

[0098] A condenser is installed between the vacuum system and the stirred tank to capture the extracted volatile substances.

[0099] Comparative Example 1: The difference between this comparative example and Example 1 is that no surface-treated nano-alumina was added when preparing the epoxy encapsulant in this comparative example.

[0100] Comparative Example 2 differs from Example 1 in that hydrogenated castor oil derivative thixotropic agent was not added during the preparation of the epoxy encapsulant in this comparative example.

[0101] Comparative Example 3 differs from Example 1 in that the nano-alumina was not surface-treated in this comparative example.

[0102] Comparative Example 4 differs from Example 1 in that γ-glycidoxypropyltrimethoxysilane was not added when preparing the epoxy encapsulating adhesive in this comparative example.

[0103] The epoxy encapsulants prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance tests. The test items and test methods are as follows:

[0104] Volume resistivity testing was conducted using a three-electrode system under a DC voltage of 500V and a test time of 60 seconds. The resistance value was measured after the voltage stabilized, and the volume resistivity was calculated.

[0105] For the water absorption test, the sample was soaked in distilled water for 24 hours at room temperature of 25°C. After drying and weighing, the sample was soaked in water again, removed and the surface moisture was wiped off. The percentage increase in mass was then calculated.

[0106] For flame retardancy testing, in a nitrogen-oxygen mixture with an initial oxygen concentration of 21%, the oxygen concentration is adjusted until the sample can burn continuously for 3 minutes or 50 mm in length, and the oxygen index is calculated.

[0107] The bond strength was tested using a universal testing machine.

[0108] The test data of the epoxy encapsulants prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below:

[0109]

[0110] By comparing and analyzing the data in the table, it can be seen that the epoxy encapsulants prepared using the processes in Examples 1-3 have significantly better performance than those prepared using the processes in Comparative Examples 1-4. This indicates that the present invention, through the synergistic combination of bisphenol A type epoxy resin and phenolic epoxy resin, and the ring-opening reaction with anhydride curing agents, forms a dense three-dimensional cross-linked network structure, sealing the pores between molecular chains and blocking charge migration paths, thereby improving the electrical insulation performance of the epoxy encapsulant. Simultaneously, the introduction of polysulfide rubber toughening agents enhances the flexibility and impact resistance of the colloid, improving the reliability of the encapsulation. The nano-alumina, modified with plasma treatment and silane coupling agent, enhances its surface activity, forming a stronger interfacial bond with the epoxy resin matrix. This reduces microcracks and voids at the interface, avoids the risk of breakdown caused by localized electric field concentration, strengthens insulation, and improves the overall mechanical strength of the encapsulant. Vacuum degassing and pressure filtration steps, under strictly controlled temperature and humidity, remove air bubbles and impurities from the colloid, ensuring its uniformity and density. Combined with microencapsulation technology of latent curing accelerators, the curing process is stable and controllable, improving the adhesive strength and long-term stability of the encapsulant.

[0111] By comparing and analyzing the relevant data in the table, it can be seen that the epoxy encapsulant prepared by the molding process of this invention has good electrical insulation, low moisture absorption, flame retardancy and high bonding strength.

[0112] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An epoxy encapsulating adhesive for a sensor, characterized in that: Made from the following raw materials in parts by weight: 40-60 parts of bisphenol A type epoxy resin, 20-30 parts of phenolic epoxy resin, 25-35 parts of acid anhydride curing agent, 0.5-2 parts of latent curing accelerator, 15-25 parts of nano alumina surface-treated with silane coupling agent, 1-3 parts of hydrogenated castor oil derivative thixotropic agent, 2-5 parts of γ-glycidyl etheroxypropyltrimethoxysilane, and 3-8 parts of polysulfide rubber toughening agent. The nano-alumina has a particle size of 20-50 nm, and its surface treatment process includes: Nano-alumina is placed in a plasma treatment device and treated with 200-400W power for 10-30 minutes under an argon atmosphere. Then it is immediately immersed in an ethanol solution of 5wt% γ-glycidoxypropyltrimethoxysilane and stirred at 60-70℃ for 2-4 hours. After filtration, washing and drying, it is obtained.

2. The epoxy encapsulating adhesive for a sensor according to claim 1, characterized in that: The bisphenol A type epoxy resin has an epoxy equivalent of 180-200 g / eq, and the phenolic epoxy resin has an epoxy equivalent of 160-180 g / eq.

3. The epoxy encapsulating adhesive for a sensor according to claim 1, characterized in that: The anhydride curing agent is one or more combinations of methyl hexahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, or hexahydrophthalic anhydride.

4. The epoxy encapsulating adhesive for a sensor according to claim 1, characterized in that: The latent curing accelerator is a microencapsulated product of 2-methylimidazole, 2-phenylimidazole or 2-ethyl-4-methylimidazole, wherein the wall material of the microcapsule is polyurethane and the core material content is 60-80 wt%.

5. The epoxy encapsulating adhesive for a sensor according to claim 1, characterized in that: The polysulfide rubber toughening agent has a molecular weight of 3000-6000 and a mercaptan content of 2-5 wt%.

6. A method for preparing an epoxy encapsulating adhesive for sensors, used to prepare the epoxy encapsulating adhesive for sensors according to any one of claims 1-5, characterized in that: Includes the following steps: Step 1: Premix epoxy resin base material. Add bisphenol A type epoxy resin and phenolic epoxy resin to a planetary stirring kettle with a heating jacket and vacuum system. Heat to 70-80℃ and stir at 100-200 rpm for 20-40 minutes until the mixture is uniform. Step 2: Dispersion at one time. The surface-treated nano-alumina is slowly added to the epoxy resin base material obtained in Step 1 under vacuum. During the addition process, the temperature inside the vessel is maintained at 70-80℃ and the vacuum degree is not lower than -0.095MPa. After the addition is completed, the stirring speed is increased to 400-600rpm and stirring is continued for 60-90 minutes. Step 3: Secondary mixing. Cool the mixture obtained in Step 2 to 40-50℃, and add the acid anhydride curing agent, hydrogenated castor oil derivative thixotropic agent, γ-glycidyl etheroxypropyltrimethoxysilane and polysulfide rubber toughening agent in sequence. Stir at 200-300 rpm for 30-45 minutes. Step 4: Final mixing and degassing. Add the latent curing accelerator to the mixture obtained in Step 3, stir at 100-200 rpm for 15-25 minutes, then turn on the vacuum system to maintain the vacuum degree in the reactor below -0.098 MPa, and stir at low speed at 40-50℃ for 60-120 minutes to degas, so as to obtain a uniform epoxy encapsulating colloid. Step 5: Filtration and packaging. The colloid after degassing in step 4 is filtered under pressure through a 200-300 mesh filter and then packaged under anhydrous and oxygen-free conditions.

7. The method for preparing an epoxy encapsulating adhesive for sensors according to claim 6, characterized in that: The nano-alumina mentioned in step two is added at a uniform rate over 20-30 minutes using a screw feeder.

8. The method for preparing an epoxy encapsulating adhesive for sensors according to claim 6, characterized in that: The defoaming process described in step four consists of two stages: In the first stage, degassing is performed at a vacuum of -0.095MPa to -0.098MPa for 30-60 minutes. In the second stage, the rotation speed is reduced to 50-100rpm, and degassing continues for another 30-60 minutes.

9. The method for preparing an epoxy encapsulating adhesive for sensors according to claim 6, characterized in that: The pressure of the pressurized filtration in step five is 0.2-0.4 MPa, and the relative humidity of the filtration environment is controlled below 10% by a dehumidification system; The filter used is a 300-mesh double-layer stainless steel sintered mesh. The filtration process is carried out in a closed, insulated pipe, with the pipe temperature maintained at 45-55℃.

10. The epoxy encapsulating adhesive for sensors according to claim 6 and its preparation method, characterized in that: The planetary mixing vessel has a double-frame mixing blade with a revolution speed of 10-30 rpm and a rotation speed of 100-600 rpm. The jacket of the stirred tank uses hot oil as the heat transfer medium, and the temperature control accuracy is ±1℃. A condenser is installed between the vacuum system and the stirred tank to capture the extracted volatile substances.

Images