Epoxy resin composite material for varistor encapsulation and preparation method thereof, encapsulation method, and encapsulated varistor

Abstract

The present application relates to the technical field of varistor packaging, and specifically discloses an epoxy resin composite material for varistor packaging, a preparation method thereof, a packaging method, and a packaged varistor. The epoxy resin composite material includes the following raw materials in parts by weight: 25-35 parts of epoxy resin, 5-10 parts of curing agent, 50-70 parts of modified silicon micropowder, 0.3-0.8 parts of pigment, 2.5-3.5 parts of flame retardant, 1.5-2.5 parts of toughening agent, and 2-4 parts of other auxiliary agents; the preparation method of modified silicon micropowder includes the step of modifying the silicon micropowder with silicone oil. The packaged varistor obtained by the epoxy resin composite material and packaging method of the present application has excellent ability to withstand high temperatures and is not easy to expand and burst.

Description

Technical Field

[0001] The present application relates to the technical field of varistor packaging, and more specifically, to an epoxy resin composite material for varistor packaging and a preparation method thereof, a packaging method, and a packaged varistor. Background Art

[0002] MOV varistors (Metal Qxide Varistors) are generally used as protective resistors. Their main function is to limit and absorb overvoltage in the circuit to protect other electronic components from damage. Under normal operating voltage, their resistance is very large and hardly affects the normal operation of the circuit; however, under overvoltage, the resistance of the varistor will decrease rapidly, forming a low-impedance path to conduct the overvoltage to the ground to protect other electronic components. When a large current instantaneously impacts the varistor, instantaneous heat will also be generated, causing the packaging material encapsulated outside the varistor to expand rapidly or even rupture due to the instantaneous heat.

[0003] When encapsulating a varistor in the conventional method, the encapsulation method used is: 1. Prepare epoxy resin encapsulation material, the raw materials for preparing the epoxy resin encapsulation material include 40 parts of epoxy resin, 9.5 parts of curing agent, 33.5 parts of filler, 0.7 parts of pigment and 16.3 parts of other additives; mix the raw materials for preparing the epoxy resin, extrude the raw material mixture with an extruder in a molten state, then press the sheet and cool it, and then crush, grade and mix and sieve to obtain a powdered encapsulation material. 2. After heating the varistor chip to be encapsulated, immerse it in the powdered encapsulation material; then take out the chip, the outer surface of the chip is adhered to the powdered encapsulation material, and place it in a 150°C oven or baking oven for natural leveling. 3. Repeat step 2, after multiple "immersion-natural leveling" steps, solidify and obtain the encapsulated varistor.

[0004] However, the packaging material of the varistor packaged by the above method is prone to rapid expansion, bursting, or even burning when subjected to a large current instantaneous impact. Summary of the invention

[0005] In order to alleviate the situation where the varistor packaging material rapidly expands and bursts when the varistor is subjected to a sudden large current shock, the present application provides an epoxy resin composite material for varistor packaging and a preparation method, a packaging method, and a packaged varistor.

[0006] In a first aspect, the present application provides an epoxy resin composite material for varistor encapsulation, which adopts the following technical solution:

[0007] An epoxy resin composite material for varistor encapsulation, the epoxy resin composite material comprising the following raw materials in parts by weight: 25-35 parts of epoxy resin, 5-10 parts of curing agent, 50-70 parts of modified silicon powder, 0.3-0.8 parts of pigment, 2.5-3.5 parts of flame retardant, 1.5-2.5 parts of toughening agent, and 2-4 parts of other additives;

[0008] The preparation method of the modified silicon micropowder comprises the step of modifying the silicon micropowder with organic silicone oil.

[0009] The traditional process of packaging varistor is as described in the background technology: after obtaining the powdered varistor packaging material, heat the chip of the varistor to be packaged and immerse it in the powdered packaging material, then take it out, and place the chip with the powdered packaging material adhered to the outer surface in a 150°C oven or baking oven for natural leveling, and repeat the steps of "immersing in powdered packaging material + melt leveling" 2-3 times, solidify, and obtain a packaged varistor. In this process, since the varistor is packaged in a natural leveling manner, it is necessary to require the packaging material to have excellent leveling properties, which means that in this scheme, the amount of epoxy resin added as the organic phase is relatively large, while the amount of filler used in the inorganic phase is relatively small; otherwise, it will seriously affect the leveling properties of the packaging material, making it impossible to successfully complete the packaging of the varistor.

[0010] However, the packaged varistor obtained by the above process has the problem of "the packaging material is prone to expansion and bursting when a large current impacts" during service. The reasons for this are: the thermal conductivity of epoxy resin is poor, and it is difficult to heat up instantly after a large current impact, and the heat is difficult to dissipate quickly, which eventually leads to rapid expansion and bursting of the packaging material.

[0011] By adopting the above technical solution, the previous "natural leveling + curing" process is changed to the current "molding + curing" process. Then, 1. The process significantly reduces the leveling requirements of the packaging material, so the amount of organic matter such as epoxy resin added in the packaging material can be significantly reduced, and the amount of inorganic phases such as fillers can be significantly increased; and the thermal conductivity of the filler is significantly better than that of the epoxy resin. When a large current impacts the varistor, even if a large amount of heat is generated instantaneously, it can be well conducted, thereby significantly alleviating the possibility of expansion and bursting of the packaging material. 2. After the amount of epoxy resin and the like is significantly reduced, the amount of bubbles caused by material mixing will also be significantly reduced. Further combined with the molding process, a large number of bubbles in the packaging material will also be removed under pressure, thereby significantly alleviating the situation where the bubbles burst due to rapid temperature rise, and then cause the packaging material to burst. Therefore, the present application synergistically reduces the probability of expansion and bursting of the varistor packaging material when the varistor is in service by improving the raw material ratio and process method. 3. In the present application, modified silica powder is selected as the inorganic filler. The reason is that if silica powder, as an inorganic phase, is mixed in large quantities in the epoxy resin of the organic phase, there will be certain problems with system compatibility and material integrity after molding. To address this problem, the silica powder is modified with silicone oil in advance to make it have relatively excellent compatibility with the organic phase, so as to reduce the probability of expansion and bursting of the packaged varistor during service.

[0012] Optionally, the method for preparing the modified silicon micropowder comprises the following steps:

[0013] Step I, dissolving the organic silicone oil in a first solvent, adding silicon micropowder to obtain a silicon micropowder dispersion; the mass ratio of the organic silicone oil to the silicon micropowder is (0.13-0.3):1;

[0014] Step II: ultrasonically disperse the silicon micropowder dispersion for 30-60 minutes, remove the first solvent, and dry to obtain modified silicon micropowder.

[0015] By adopting the above technical solution, the silicon micropowder and the silicone oil are fully mixed and dispersed by ultrasonic dispersion, so that the silicon micropowder is fully coated by the silicone oil. The silicon micropowder coated with silicone oil can significantly improve its compatibility with epoxy resin; therefore, even if there is a large amount of silicon micropowder in the packaging material, a packaging material with excellent performance can still be prepared by the method of the present application.

[0016] Optionally, the following steps are further included before molding: mixing the epoxy resin, the modified silica powder and the second solvent, reacting at 140-160° C., washing with water and drying to obtain a resin-filler mixture.

[0017] By adopting the above technical solution, the modified silicon micropowder and epoxy resin are pre-mixed, which has the following effects: 1. The modified silicon micropowder and epoxy resin are mixed more fully and evenly; 2. The silicone oil and epoxy resin in the modified silicon micropowder react under the above conditions, and the silicone oil and epoxy resin therein will further react to form a network structure with appropriate cross-linking, thereby more stably coating and dispersing the silicon micropowder; 3. After the silicone oil and epoxy resin react, the silicon oxygen bond replaces part of the carbon oxygen bond, and the bond energy of the silicon oxygen bond is significantly greater than the bond energy of the carbon oxygen bond, so it plays a shielding role on the connected groups, further improving the heat resistance of the epoxy resin. The use of this packaging material for varistor packaging can further promote the improvement of the problem of expansion and bursting of the packaging material.

[0018] Optionally, the reaction time is 20-26 hours.

[0019] Optionally, other additives are selected from any one or more of a leveling agent, a curing accelerator and a coupling agent;

[0020] Preferably, the leveling agent is selected from any one or more of acrylates and hydrogenated castor oil;

[0021] Preferably, the curing accelerator is selected from any one or more of imidazoles, organic phosphine compounds, ureas, fluoroborates and quaternary ammonium salts;

[0022] The flame retardant is a flame retardant that does not contain aluminum hydroxide;

[0023] Preferably, the flame retardant is selected from any one or more of phosphorus flame retardants, silicon flame retardants, nitrogen flame retardants and metal boride flame retardants.

[0024] Preferably, the phosphorus flame retardant is selected from any one or more of organic phosphides, organic phosphonates and phosphites;

[0025] Further preferably, the organic phosphonate is selected from any one or more of condensation-type halogen-free phosphates, tricresyl phosphate, triphenyl phosphate, tricresyl phosphate, butylbenzene phosphate, propylbenzene phosphate, phenoxyphosphine, phenoxy polyphosphazene, dimethyl methylphosphonate, diethyl ethylphosphonate, isopropylphenyl phosphate, tert-butylbenzene diyl phosphate, tetraarylarylene bisphosphate, resorcinol phosphate, tetraphenyl bisphenol A-diphosphate and pentaerythritol melamine phosphate.

[0026] The reason why metal hydroxide flame retardants are not selected by adopting the above technical solution is that metal hydroxides, such as aluminum hydroxide and magnesium hydroxide, are easy to decompose and produce gas at high temperature, and the gas will also burst at high temperature. Whether it is gas expansion or gas explosion, it will aggravate the expansion and explosion of the packaging material outside the varistor during service. Therefore, the selection of non-metal hydroxide flame retardants can further alleviate the problem of expansion and explosion of the packaging material of the varistor under instantaneous large current impact.

[0027] Optionally, the epoxy resin is selected from any one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, distyrene epoxy resin, biphenyl epoxy resin, polyether modified epoxy resin, silicone modified epoxy resin and polyurethane modified epoxy resin.

[0028] Optionally, the curing agent is a phenolic curing agent.

[0029] Optionally, the silicon micropowder is crystalline silicon micropowder or molten silicon micropowder; preferably, the silicon micropowder is molten silicon micropowder.

[0030] By adopting the above technical solution, compared with crystalline silicon powder, molten silicon powder has a lower linear thermal expansion coefficient, so the volume expansion is small under instantaneous high temperature, thereby improving the expansion and bursting of the packaging material.

[0031] Optionally, the first solvent is selected from any one or more of ethanol and xylene.

[0032] Optionally, the silicone oil is polyphenylmethylsiloxane.

[0033] In a second aspect, the present application provides a method for preparing the above-mentioned epoxy resin composite material for varistor encapsulation, which adopts the following technical solution:

[0034] A method for preparing the epoxy resin composite material for varistor encapsulation, the preparation method comprising the following steps: step S1, mixing the epoxy resin, curing agent, modified silicon powder, pigment, flame retardant, toughening agent and other additives to obtain a raw material mixture;

[0035] Step S2: The raw material mixture is subjected to internal mixing, extrusion, tableting, cooling, crushing and screening to obtain an epoxy resin composite material.

[0036] In the above scheme, the internal kneading in step S2 is to make the raw materials fully mixed and uniform; and because the raw materials are viscous after internal kneading, they are transferred by extrusion; and the surface area is increased by tableting to facilitate cooling, so the tableting process is mainly to achieve the purpose of increasing the heat dissipation area; after cooling, further crushing is carried out, and after crushing, further screening is carried out to obtain powder particles of suitable particle size. Screening may include the steps of air separation and mixed drying. Air separation is mainly to obtain the target powder with appropriate particle size, and mixed screening can further remove large particles of impurities in the powder.

[0037] Optionally, step S1 specifically includes: mixing and dispersing the epoxy resin and the modified silica powder in a second solvent, reacting at 140-160° C., and drying to obtain a resin-filler mixture; and mixing the resin-filler mixture with other raw materials to obtain a raw material mixture.

[0038] Optionally, the reaction time is 20-26h.

[0039] Optionally, the particle size of the epoxy resin composite material is less than 150 μm.

[0040] In a third aspect, the present application provides a varistor packaging method using the above-mentioned epoxy resin composite material for varistor packaging, which adopts the following technical solution:

[0041] A method for packaging a varistor using the epoxy resin composite material for packaging a varistor, the packaging method comprising the following steps:

[0042] The varistor and the epoxy resin composite material are placed in a mold, molded at a pressure of 15-25 MPa, and cured at a temperature of 120-170°C.

[0043] By adopting the above technical solution, high pressure molding is used to effectively eliminate bubbles existing in the raw materials and shape the packaging material.

[0044] In the above scheme, the steps of molding and curing can be performed simultaneously; or the molding can be performed first and then curing.

[0045] Optionally, the molding time is 5-15 minutes; the curing time is 45-75 minutes.

[0046] In a fourth aspect, the present application provides a packaged varistor, which adopts the following technical solution:

[0047] A packaged varistor is prepared by the varistor packaging method.

[0048] In summary, this application has the following beneficial effects:

[0049] 1. The packaging material (i.e., epoxy resin composite material) of the present application is prepared by molding, so the bubbles in the raw materials can be effectively removed, and the deformation of the packaged varistor caused by the expansion of bubbles when heated can be reduced; in addition, since the varistor is packaged by molding, the leveling requirements of the system formed by the raw materials are significantly reduced, the amount of inorganic filler is significantly increased, and the amount of organic material is significantly reduced, thereby significantly improving the thermal conductivity of the packaging material and avoiding the deformation of the packaged varistor caused by a large amount of heat accumulation.

[0050] 2. The inorganic filler selected in the present application is silicon micropowder, but after being modified with organic silicone oil, the compatibility of silicon micropowder and epoxy resin can be significantly improved to obtain a packaging material with excellent performance.

[0051] 3. When the modified silica powder of the present application is mixed with the epoxy resin, the silicone oil and the epoxy resin are reacted by heating to further modify the epoxy resin and improve the thermal conductivity of the resin. In addition, the silicone oil itself is coated on the outside of the silica powder, and the pre-reaction of the modified silica powder and the epoxy resin will also make the dispersion of the epoxy resin and the silica powder more stable, and the coating of the silica powder by the epoxy resin will be more stable and firm. DETAILED DESCRIPTION

[0052] The present application is further described in detail below in conjunction with the examples. It is particularly noted that if no specific conditions are specified in the following examples, the experiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.

[0053] Preparation example of modified silicon powder

[0054] Preparation Example 1

[0055] The preparation method of modified silicon micropowder is:

[0056] Step I: dissolving polyphenylmethylsiloxane in xylene, and then adding 1000 g of molten silicon powder to obtain a silicon powder dispersion, wherein the mass ratio of polyphenylmethylsiloxane to molten silicon powder is 0.13:1.

[0057] Step II: ultrasonically disperse the silicon micropowder dispersion obtained in step I for 60 minutes, then distill to remove xylene to obtain a solid, and dry to obtain modified silicon micropowder.

[0058] Preparation Example 2

[0059] The preparation method of modified silicon micropowder is:

[0060] Step I: dissolving polyphenylmethylsiloxane in xylene, and then adding 1000 g of molten silicon powder to obtain a silicon powder dispersion, wherein the mass ratio of polyphenylmethylsiloxane to molten silicon powder is 0.24:1.

[0061] Step II: ultrasonically disperse the silicon micropowder dispersion obtained in step I for 45 minutes, then distill to remove xylene to obtain a solid, and dry to obtain modified silicon micropowder.

[0062] Preparation Example 3

[0063] The preparation method of modified silicon micropowder is:

[0064] Step I: dissolving polyphenylmethylsiloxane in xylene, and then adding 1000 g of molten silicon powder to obtain a silicon powder dispersion, wherein the mass ratio of polyphenylmethylsiloxane to molten silicon powder is 0.3:1.

[0065] Step II: ultrasonically disperse the silicon micropowder dispersion obtained in step I for 30 minutes, then distill to remove xylene to obtain a solid, and dry to obtain modified silicon micropowder.

[0066] Preparation Example 4

[0067] The preparation method of modified silicon micropowder is:

[0068] Step I: dissolving polyphenylmethylsiloxane in xylene, and then adding 1000 g of molten silicon powder to obtain a silicon powder dispersion, wherein the mass ratio of polyphenylmethylsiloxane to molten silicon powder is 0.24:1.

[0069] Step II: Stir and mix the silicon micropowder dispersion obtained in step I for 45 minutes, then distill to remove xylene to obtain a solid, and dry to obtain modified silicon micropowder.

[0070] Example

[0071] Example 1

[0072] An epoxy resin composite material for varistor packaging, the raw material components of which are:

[0073] 250g of bisphenol A epoxy resin, 50g of curing agent 2,4,6-tris(dimethylaminomethyl)phenol, 600g of modified silica powder, 3g of carbon black, 25g of flame retardant phenoxyphosphine, 15g of toughening agent polyazelaic anhydride, 20g of other additives (specifically: 15g of GLP503 polyacrylate, 5g of dimethylimidazole). The modified silica powder is prepared according to the modified silica powder preparation example 1.

[0074] A method for preparing an epoxy resin composite material for varistor packaging, the specific steps are:

[0075] Step S1, mix bisphenol A epoxy resin, modified silica powder and xylene, react at 140°C for 26 hours, filter, dry the solid, and obtain a resin filler mixture. Mix the resin filler mixture with curing agent 2,4,6-tris(dimethylaminomethyl)phenol, carbon black, flame retardant phenoxyphosphine, toughening agent polyazelaic anhydride, GLP503 polyacrylate and dimethylimidazole, stir evenly, and obtain a raw material mixture for standby use.

[0076] Step S2, kneading and extruding the raw material mixture at 130° C., then cooling it after tableting it on a tablet press, and then crushing and air-selecting it to obtain a powdery epoxy resin composite material crude product, and then screening the epoxy resin composite material crude product with an 80-mesh sieve to obtain an epoxy resin composite material with a particle size less than 150 μm.

[0077] A method for packaging a varistor using the epoxy resin composite material, comprising the following specific steps:

[0078] The varistor and epoxy resin composite material were placed in a mold and molded at a pressure of 15 MPa for 15 minutes; then cured at 120° C. for 75 minutes to obtain a packaged varistor.

[0079] Example 2

[0080] An epoxy resin composite material for varistor packaging, the raw material components of which are:

[0081] 300g of bisphenol A epoxy resin, 75g of curing agent 2,4,6-tris(dimethylaminomethyl)phenol, 650g of modified silica powder, 5g of carbon black, 30g of flame retardant phenoxyphosphine, 20g of toughening agent polyazelaic anhydride, 30g of other additives (specifically: 15g of GLP503 polyacrylate, 15g of curing accelerator). The modified silica powder is prepared according to the modified silica powder preparation example 2.

[0082] A method for preparing an epoxy resin composite material for varistor packaging, the specific steps are:

[0083] Step S1, mix bisphenol A epoxy resin, modified silica powder and xylene, react at 150°C for 24 hours, filter, dry the solid, and obtain a resin filler mixture. Mix the resin filler mixture with curing agent 2,4,6-tris(dimethylaminomethyl)phenol, carbon black, flame retardant phenoxyphosphine, toughening agent polyazelaic anhydride, GLP503 polyacrylate and dimethylimidazole, stir evenly, and obtain a raw material mixture for standby use.

[0084] Step S2, kneading and extruding the raw material mixture at 135° C., then cooling it after tableting it on a tablet press, and then crushing and air-selecting it to obtain a powdery epoxy resin composite material crude product, and then screening the epoxy resin composite material crude product with an 80-mesh sieve to obtain an epoxy resin composite material with a particle size less than 150 μm.

[0085] A method for packaging a varistor using the epoxy resin composite material, comprising the following specific steps:

[0086] The varistor and the epoxy resin composite material are placed in a mold and molded at a pressure of 20 MPa for 10 minutes; then cured at 150° C. for 60 minutes to obtain a packaged varistor.

[0087] Example 3

[0088] An epoxy resin composite material for varistor packaging, the raw material components of which are:

[0089] 350g of bisphenol A epoxy resin, 100g of curing agent 2,4,6-tris(dimethylaminomethyl)phenol, 700g of modified silica powder, 8g of carbon black, 35g of flame retardant phenoxyphosphine, 25g of toughening agent polyazelaic anhydride, 40g of other additives (specifically: 20g of GLP503 polyacrylate, 20g of curing accelerator). The modified silica powder is prepared according to the modified silica powder preparation example 3.

[0090] A method for preparing an epoxy resin composite material for varistor packaging, the specific steps are:

[0091] Step S1, mix bisphenol A epoxy resin, modified silica powder and xylene, react at 160°C for 20 hours, filter, dry the solid, and obtain a resin filler mixture. Mix the resin filler mixture with curing agent 2,4,6-tris(dimethylaminomethyl)phenol, carbon black, flame retardant phenoxyphosphine, toughening agent polyazelaic anhydride, GLP503 polyacrylate and dimethylimidazole, stir evenly, and obtain a raw material mixture for standby use.

[0092] Step S2, kneading and extruding the raw material mixture at 138° C., then cooling it after tableting it on a tablet press, and then crushing and air-selecting it to obtain a powdery epoxy resin composite material crude product, and then screening the epoxy resin composite material crude product with an 80-mesh sieve to obtain an epoxy resin composite material with a particle size less than 150 μm.

[0093] A method for packaging a varistor using the epoxy resin composite material, comprising the following specific steps:

[0094] The varistor and epoxy resin composite material were placed in a mold and molded at a pressure of 25 MPa for 5 minutes; then cured at 170° C. for 45 minutes to obtain a packaged varistor.

[0095] Example 4

[0096] The difference between Example 4 and Example 2 is that the sources of the modified silicon micropowder for preparing the epoxy resin composite material for varistor encapsulation are different; the modified silicon micropowder of Example 4 is derived from the modified silicon micropowder preparation example 4.

[0097] Embodiment 5-6

[0098] The difference between Example 5-6 and Example 2 is that the amount of modified silicon micropowder used in preparing the epoxy resin composite material for varistor encapsulation is different; specifically, the amount of modified silicon micropowder used in Example 5 is 500g, and the amount of modified silicon micropowder used in Example 6 is 700g.

[0099] Example 7

[0100] The difference between this embodiment and embodiment 2 is that the preparation method of the epoxy resin composite material is different, which is as follows:

[0101] A method for preparing an epoxy resin composite material for varistor packaging, the specific steps are:

[0102] Step S1, mix bisphenol A epoxy resin, modified silica powder, curing agent 2,4,6-tris(dimethylaminomethyl)phenol, carbon black, flame retardant phenoxyphosphine, toughening agent polyazelaic anhydride, GLP503 polyacrylate and dimethylimidazole, stir evenly to obtain a raw material mixture for standby use.

[0103] Step S2, kneading and extruding the raw material mixture at 135° C., then cooling it after tableting it on a tablet press, and then crushing and air-selecting it to obtain a powdery epoxy resin composite material crude product, and then screening the epoxy resin composite material crude product with an 80-mesh sieve to obtain an epoxy resin composite material with a particle size less than 150 μm.

[0104] A method for packaging a varistor using the above-mentioned epoxy resin composite material is the same as that in Example 2.

[0105] Comparative Example

[0106] Comparative Example 1-2

[0107] The difference between Comparative Examples 1-2 and Example 2 is that different amounts of modified silicon micropowder are used in preparing the epoxy resin composite material; specifically, the amount of modified silicon micropowder used in Comparative Example 1 is 400 g, and the amount of modified silicon micropowder used in Comparative Example 2 is 800 g.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 2 is that the modified silicon micropowder is replaced by silicon micropowder of equal weight for preparing the epoxy resin composite material.

[0110] Comparative Example 4

[0111] An epoxy resin composite material for varistor packaging, the raw material components of which are:

[0112] 400g bisphenol A epoxy resin, 95g curing agent 2,4,6-tris(dimethylaminomethyl)phenol, 335g fused silica powder, 7g carbon black, 30g flame retardant phenoxyphosphine, 85g aluminum hydroxide, 15g toughening agent polyazelaic anhydride, 10g GLP503 polyacrylate, 3g dimethylimidazole, and 2g titanium dioxide.

[0113] A method for preparing an epoxy resin composite material for varistor packaging, the specific steps are:

[0114] Step 1: Mix bisphenol A epoxy resin, fused silica powder, curing agent 2,4,6-tris(dimethylaminomethyl)phenol, carbon black, flame retardant phenoxyphosphine, aluminum hydroxide, toughening agent polyazelaic anhydride GLP503, polyacrylate, dimethylimidazole and titanium dioxide, stir evenly to obtain a raw material mixture for later use.

[0115] Step 2: The raw material mixture is extruded at 135° C., and then the mixture is compressed on a tablet press and cooled, and then crushed and air-selected to obtain a powdered epoxy resin composite material crude product, and then the epoxy resin composite material crude product is screened with an 80-mesh sieve to obtain an epoxy resin composite material with a particle size of less than 150 μm.

[0116] A method for packaging a varistor using the epoxy resin composite material, comprising the following specific steps:

[0117] The varistor is heated to 150°C, and then immersed in the raw material mixture for 1 minute. After being taken out, the surface of the varistor is adhered to the powdered epoxy resin composite material; then it is placed in an oven at 150°C for natural leveling; after being taken out, it is immersed in the raw material mixture for 1 minute, and then placed in an oven at 150°C for natural leveling and then cured; thus, a packaged varistor is obtained.

[0118] Performance Testing

[0119] 1. Carry out power frequency withstand test on the packaged varistor. The specific results are shown in Table 1.

[0120] Table 1 Power frequency withstand test results of different packages

[0121]

[0122]

[0123] It can be seen from the data results in Table 1 that, compared with the conventional packaging material of Comparative Example 4, the varistor encapsulated by the epoxy resin composite material and packaging method of the present application has very excellent flame retardant properties. The encapsulated varistor can have a long power frequency tolerance time (more than 3 minutes) at a high temperature loading temperature (135°C). Referring to Example 2, Examples 5-6 and Comparative Examples 1-2, when preparing the packaging material, the amount of modified silicon micropowder is recommended to be in the range of 50-70 parts by weight to ensure its excellent high temperature working performance and avoid expansion, bursting and even burning. When the amount of modified silicon micropowder is small, it will directly affect the heat dissipation of the encapsulated varistor, making it prone to expansion and bursting. When the amount of modified silicon micropowder is too much, it affects the uniform dispersion of the organic phase and the inorganic phase, which ultimately causes the encapsulated varistor to be prone to local expansion and bursting.

[0124] In addition, in Example 4, when preparing the modified silicon micropowder, the modified silicon micropowder is obtained by ultrasonic dispersion, which can make the raw materials fully mixed to ensure the excellent performance of the packaging material.

[0125] In Comparative Example 3, the fused silica powder is not modified, and its compatibility and dispersibility with the organic phase are poor, which will directly affect the uniformity of the material and further affect its effect.

[0126] 2. The conditions of the power frequency withstand test of Example 2 were used to test different packaged varistors, i.e., the loading conditions were 135°C / 1000H, the loading temperature was 950-1000°C, and the power frequency loading time was 4min. 30 of each packaged varistors were tested to calculate the probability of packaged varistors being damaged in appearance. The packaged varistors being damaged in appearance refer to: any one of bubbling, cracking, smoke or burning on the outer surface of the packaged varistors, i.e., packaged varistors being damaged in appearance. The specific results are shown in Table 2.

[0127] Table 2 Deformation of different packaged varistors

[0128]

[0129] From the data in Table 2, it can be seen that the packaged varistor of the present application can still maintain a good appearance under the same power frequency tolerance conditions, that is, the packaged varistor is not easy to expand and burst under instantaneous large current. However, the data of Example 2 and Example 7 also show that when packaging the varistor, pre-mixing the modified silicon micropowder and epoxy resin and then mixing them with other raw materials can further improve the problem of appearance damage of the packaged varistor. Compared with the packaged varistor of Example 2, the probability of appearance damage of the packaged varistors of Comparative Examples 1 and Comparative Examples 2 is higher, mainly because: when the amount of modified silicon micropowder is too small, it will directly affect the heat dissipation of the packaged varistor, making it easy to expand and burst; and when the amount of modified silicon micropowder is too much, it affects the uniform dispersion of the organic phase and the inorganic phase, making the toughness of the packaging material poor, and ultimately causing the packaged varistor to easily expand and burst locally. The packaged varistor in Comparative Example 4 is prepared by conventional methods. Due to the large number of bubbles in the natural leveling process and the bubbles generated by the high-temperature decomposition of aluminum hydroxide, the existence of these bubbles will expand and burst at high temperatures, thereby causing the shape of the packaged varistor to change or even break. In addition, the reduction in the amount of inorganic filler will also make the thermal conductivity of the packaging material poor, thereby making it impossible to effectively release the accumulated heat, aggravating the problem of appearance destruction (such as smoke, burning, etc.) of the packaged varistor.

[0130] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A varistor packaging method, characterized in that: The packaging method comprises the following steps: Place the varistor and epoxy resin composite material in a mold, press mold them at a pressure of 15-25MPa, and cure them at a temperature of 120-170℃; The epoxy resin composite material comprises the following raw materials in parts by weight: Epoxy resin 25-35 parts, curing agent 5-10 parts, modified silica powder 50-70 parts, pigment 0.3-0.8 parts, flame retardant 2.5-3.5 parts, toughening agent 1.5-2.5 parts, other additives 2-4 parts; The preparation method of the modified silicon micropowder comprises the following steps: Step I, dissolving the organic silicone oil in a first solvent, adding silicon micropowder to obtain a silicon micropowder dispersion; the mass ratio of the organic silicone oil to the silicon micropowder is (0.13-0.3):1; Step II, ultrasonically dispersing the silicon micropowder dispersion for 30-60 minutes, removing the first solvent, and drying to obtain modified silicon micropowder; The silicone oil is polyphenylmethylsiloxane; The epoxy resin composite material preparation method comprises the following steps: Step S1, mixing the epoxy resin, curing agent, modified silicon powder, pigment, flame retardant, toughening agent and other additives to obtain a raw material mixture; Step S2, the raw material mixture is subjected to internal mixing, extrusion, tableting, cooling, crushing and screening to obtain an epoxy resin composite material; Step S1 specifically includes: mixing and dispersing the epoxy resin and the modified silica powder in a second solvent, reacting at 140-160° C., and drying to obtain a resin-filler mixture; and mixing the resin-filler mixture with other raw materials to obtain a raw material mixture.

2. The varistor packaging method according to claim 1, characterized in that: The molding time is 5-15 minutes; the curing time is 45-75 minutes.

3. The varistor packaging method according to claim 1, characterized in that: When preparing the epoxy resin composite material, the reaction time in step S1 is 20-26 hours at 140-160°C.

4. The varistor packaging method according to claim 1, characterized in that: Other additives are selected from any one or more of leveling agents, curing accelerators and coupling agents; The leveling agent is selected from any one or more of acrylates and hydrogenated castor oil; The curing accelerator is selected from any one or more of imidazoles, organic phosphine compounds, ureas, fluoroborates and quaternary ammonium salts; The flame retardant is a flame retardant that does not contain hydroxide.

5. A packaged varistor, characterized in that: The packaged varistor is prepared by the varistor packaging method according to any one of claims 1 to 4.

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