Conductive adhesive, and preparation method and application thereof

Abstract

The application belongs to the technical field of conductive glue, and particularly relates to a conductive glue, a preparation method and application thereof, wherein the conductive glue is made of the following raw materials in parts by weight: 40-60 parts of synthetic acrylic resin, 5-15 parts of epoxy resin, 25-45 parts of conductive filler, 5-15 parts of latent curing aid, 80-120 parts of diluent and 5-8 parts of auxiliary agent. By adding the latent curing aid, the application can reduce the potential possibility of the reaction of the acrylic resin and the epoxy resin at room temperature, thereby improving the storage effect of the conductive glue, improving the overall performance of the electronic product and meeting different application scenarios with different requirements. The preparation method directly mixes the raw materials such as the acrylic resin, the epoxy resin, the conductive filler, the auxiliary agent, the diluent and the latent curing aid uniformly in the preparation process without the need of separation and storage, thereby reducing the production cost, simplifying the use process of the user, improving the production efficiency of the conductive glue and the product quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of conductive glue, and particularly relates to a conductive glue and a preparation method and application thereof. BACKGROUND

[0002] With the progress of society and the development of technology, electronic products are more and more widely used in our daily life, and the requirements for product performance are also higher and higher. Especially in some key fields such as communication, medical treatment, military affairs and the like, the stability and reliability of components are required more strictly. Shielding function is one of important means to ensure the stable work of components. Through shielding, the influence of external electromagnetic interference on components can be effectively prevented, and the performance and stability of products can be improved. For example, in electronic devices such as mobile phones, if components are interfered by external interference, problems such as screen flickering, black screen, and good and bad shooting effects may be caused, which seriously affect the user experience. Therefore, strengthening the shielding function of electronic components has important significance for improving the overall performance of electronic products and user experience.

[0003] At present, the conductive glue film used for shielding and conductive grounding in the market is a commonly used shielding material, which is mainly used for conductive grounding and shielding of electronic components. It has good conductive performance and bonding performance, and can effectively isolate components from the outside world to prevent the invasion of electromagnetic interference. The existing conductive glue film has low curing activity. These products require refrigeration to extend their shelf life during use. It is difficult to ensure the performance stability and operability of the product at room temperature. The main body of some products needs to be separated from the curing agent, and mixing is carried out during preparation to avoid premature reaction and curing of the conductive glue. This brings inconvenience to the production of users, thereby affecting the efficiency and limiting the application scenarios of the conductive glue. Therefore, it is necessary to develop a conductive glue which can prolong the storage time without affecting its performance, a preparation method and application thereof, so as to improve the overall performance of electronic products and meet different application scenarios of different requirements. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the above-mentioned conductive glue and provide a conductive glue.

[0005] The application adopts the following technical solutions:

[0006] A conductive glue is prepared from the following raw materials by weight: 40-60 parts of synthetic acrylic resin, 5-15 parts of epoxy resin, 25-45 parts of conductive filler, 5-15 parts of latent curing aid, 80-120 parts of diluent, and 5-8 parts of auxiliary agent.

[0007] Specifically, the synthetic acrylic resin has good adhesion and weather resistance, and can provide a stable matrix for the conductive adhesive. In addition, the epoxy resin has excellent adhesion and mechanical strength, and the addition of the epoxy resin to the conductive adhesive can further improve the adhesion and durability of the adhesive. Furthermore, by adding conductive fillers, the resistivity of the adhesive can be significantly reduced, and the conductive performance can be improved. Preferably, the latent curing aid can adjust the curing speed, hardness, and temperature resistance of the conductive adhesive at different temperatures, thereby improving the storage time of the conductive adhesive at room temperature. In addition, the diluent is used to adjust the viscosity and flowability of the conductive adhesive for construction operation. In addition, the aid helps to improve the stability of the adhesive and the dispersibility of the filler, thereby improving the overall performance of the adhesive.

[0008] Further, the synthetic acrylic resin is synthesized from methyl acrylate, methyl methacrylate, glycidyl methacrylate, styrene, and methacrylic acid.

[0009] Specifically, methyl acrylate itself has good weather resistance and adhesion, and can also serve as a soft monomer to provide flexibility and adhesion of the resin; in addition, methyl methacrylate as a hard monomer can increase the hardness, wear resistance, and transparency of the resin; furthermore, glycidyl methacrylate contains epoxy groups, which can cross-link with other resins or curing agents, thereby improving the hardness, adhesion, heat resistance, and chemical resistance of the resin; in addition, styrene can increase the rigidity and heat distortion temperature of the resin, thereby improving the high-temperature stability and impact resistance of the adhesive; at the same time, the introduction of carboxyl functional groups by methacrylic acid increases the polarity and hydrophilicity of the resin, thereby adjusting the viscosity and flowability of the resin and facilitating the wetting and dispersion of the conductive fillers.

[0010] Further, the epoxy resin includes a trifunctional alicyclic epoxy resin and a bisphenol A epoxy resin.

[0011] Specifically, the trifunctional alicyclic epoxy resin has a high cross-linking density, chemical resistance, and mechanical properties, and can provide strong adhesion and durability, thereby ensuring stable performance of the conductive adhesive in various environments. At the same time, its high cross-linking density also helps to improve the shielding effect and anti-interference ability of the conductive adhesive, while having a higher glass transition temperature (Tg) and better heat resistance.

[0012] Specifically, the bisphenol A epoxy resin has good flexibility and bonding properties, chemical resistance and electrical insulation properties, and has good adhesion to various substrates, and its good physical and mechanical properties can increase the strength and toughness of the conductive adhesive and improve its durability in the application process. The bisphenol A epoxy resin and the trifunctional alicyclic epoxy resin synergistically improve the comprehensive performance of the conductive adhesive. At the same time, its good electrical insulation performance also helps to reduce the risk of electric leakage of the conductive adhesive during use.

[0013] Specifically, by adding the trifunctional alicyclic epoxy resin and the bisphenol A epoxy resin, certain flexibility can be added while maintaining good mechanical strength, thereby improving the overall mechanical properties of the conductive adhesive, while ensuring the bonding effect of the conductive adhesive on different substrates, improving its application range and reliability, and balancing the heat resistance of the two to enable the conductive adhesive to maintain good performance in high temperature environment. In addition, the trifunctional alicyclic epoxy resin with high crosslinking density and high curing temperature is mixed with the bisphenol A epoxy resin with low viscosity and low curing temperature, which is easy to process and coat.

[0014] Preferably, the ratio of the trifunctional alicyclic epoxy resin and the bisphenol A epoxy resin of the epoxy resin is 3:7-5:5. By such setting, not only the hardness and flexibility of the resin can be considered to balance the mechanical properties, but also the stability at high temperature can be improved to optimize the heat resistance. Furthermore, the adhesion to various substrates is used to enhance the bonding properties, and different curing conditions are adapted to improve the curing characteristics, and the processing performance is improved to facilitate coating and operation, which can improve the overall performance of the conductive adhesive.

[0015] Further, the conductive filler includes at least two or more of silver-coated polystyrene microspheres, modified carbon nanotubes, silver powder, and modified expanded graphite. Specifically, the silver-coated polystyrene microspheres can reduce the overall density of the material and reduce the overall cost of the conductive adhesive. By highly dispersing silver nanoparticles on the surface of the polystyrene microspheres, the high conductivity of silver and the three-dimensional structure of the polystyrene microspheres can achieve high electromagnetic interference shielding efficiency at low metal content, which helps to improve the electrical conductivity and mechanical stability of the conductive adhesive.

[0016] Specifically, the modified carbon nanotubes of the present application are obtained by chemically modifying the surface of the original carbon nanotubes. The modified carbon nanotubes have better dispersibility and compatibility with the matrix resin, thereby more effectively improving the electrical conductivity of the conductive adhesive. At the same time, the carbon nanotubes also have excellent mechanical properties and thermal stability, which can enhance the overall performance of the conductive adhesive.

[0017] Specifically, the modified carbon nanotube of the present application is a carboxylated carbon nanotube, which has better dispersibility in a solvent and can be uniformly dispersed with the modified expanded graphite. The carboxyl group can form a hydrogen bond or a covalent bond with the functional group on the surface of the modified expanded graphite, thereby enhancing the interfacial bonding force.

[0018] The preparation method of the modified carbon nanotube comprises the following steps:

[0019] P1, a concentrated nitric acid and a concentrated sulfuric acid are configured to form a mixed acid solution according to a volume ratio, and the multi-walled carbon nanotube liquid is slowly added to the mixed acid solution while being continuously stirred;

[0020] P2, ultrasonic treatment is performed at 50-80℃ for 4-6 hours, after the ultrasonic treatment is completed, heating and stirring are performed, and reflux reaction is performed at 50-60℃ for 3 hours to obtain a reaction liquid;

[0021] P3, the reaction liquid is slowly poured into a container containing deionized water, and then cooled and suction filtered, washed with a large amount of deionized water until the pH approaches 7, and the acidified carbon nanotube is vacuum dried at 70-90℃ for 12 hours to obtain the carboxylated carbon nanotube.

[0022] Specifically, the silver powder has excellent electrical conductivity and stability. In the conductive adhesive, the silver powder can provide a continuous conductive path to ensure smooth transmission of electrons. The silver powder can also increase the filling density of the conductive adhesive, thereby improving its electrical conductivity and mechanical strength. Preferably, the present application uses flaky silver powder, because the particles are in line contact or surface contact, compared with the point contact of spherical silver powder, the flaky silver powder has relatively low resistance, the specific surface area of the flaky silver powder is relatively larger than that of the spherical silver powder, and the surface activation energy is lower than that of the spherical or spherical-like silver powder, so the oxidation degree and oxidation tendency are lower. The flaky silver powder has a wider deflection range and anti-fracture stretching characteristics, which helps to enhance the anti-deformation ability of electronic components when subjected to external forces.

[0023] Specifically, the modified expanded graphite has a larger specific surface area and better dispersibility than the original graphite, forms more conductive channels in the conductive adhesive, and thus improves the electrical conductivity. At the same time, the expanded graphite also has excellent high-temperature resistance and chemical stability, so that the conductive adhesive can still maintain good performance under high temperature and harsh environment.

[0024] Further, the modified expanded graphite used in the present application is a material after ZIF-7 is compounded with expanded graphite. The modified expanded graphite after ZIF-7 is compounded with expanded graphite has significant beneficial effects as conductive filler, including improving the conductive performance, enhancing the mechanical performance, improving the thermal stability, and optimizing the interface compatibility. Specifically, the expanded graphite has a large specific surface area and a porous structure, which helps to form a conductive network in the polymer matrix, thereby reducing the percolation value and the critical volume fraction of the filler required to reach the conductive state. The ZIF-7 material has a regular pore structure and a high specific surface area, which is beneficial to improve the conductive performance. When ZIF-7 is compounded with expanded graphite, the advantages of the two will be complementary, thereby further improving the conductive performance. The lamellar structure of the expanded graphite can increase the toughness and strength of the composite material, while the porous structure of ZIF-7 helps to absorb external stress and prevent crack propagation. This synergistic effect enables the composite material to maintain good conductivity while also having excellent mechanical properties. The ZIF-7 material has high thermal stability, which helps to improve the heat resistance of the composite material. When compounded with expanded graphite, the synergistic effect of the two can further improve the thermal stability of the composite material, enabling it to maintain good conductivity and mechanical properties in high-temperature environments.

[0025] Specifically, the preparation method of the modified expanded graphite is as follows:

[0026] Q1, dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol respectively, stir vigorously, centrifuge, wash with anhydrous methanol to obtain white powder, and vacuum dry to obtain ZIF-7 crystals;

[0027] Q2, add natural flake graphite to concentrated sulfuric acid, stir uniformly, slowly add sodium nitrate, continue to stir and add potassium permanganate in batches, control the temperature between 20-30℃ to avoid violent reaction. After 4 hours of reaction, dilute with deionized water, then add hydrogen peroxide to stop the reaction; after washing and drying, put it into a high-temperature furnace, heat rapidly at 800-1000℃, and cool to obtain expanded graphite.

[0028] Q3, add ZIF-7 and expanded graphite to ethanol respectively, add polyvinylpyrrolidone and silane coupling agent, continue to stir for 1 hour, and place the mixture in an ultrasonic cleaner for ultrasonic treatment for 30 minutes;

[0029] Q4, filter the ultrasonic treated mixture, collect the solid part, wash with ethanol, and vacuum dry at 60℃ for 12 hours.

[0030] Further, the high aspect ratio of the carbon nanotubes and the hydrophilicity after carboxylation can form a uniform three-dimensional network with ZIF-7 and expanded graphite, further enhancing the electrical conductivity and mechanical strength, while providing excellent dispersibility and bonding force. The synergy of the flaky silver powder with ZIF-7 and expanded graphite can form a multi-level conductive network, further reducing the resistance and improving the electrical conductivity. The flaky structure helps to enhance the mechanical properties and thermal conductivity of the composite material. The porous structure of the modified expanded graphite helps to improve the dispersibility of the silver-coated polystyrene microspheres in the matrix, thereby improving the overall performance of the composite material. It can also prevent the oxidation and agglomeration of silver-coated polystyrene microspheres, maintaining the stability of the material.

[0031] Further, the latent curing aid includes one or more of a phenolic amine curing agent, a curing accelerator, the diluent includes one or more of butyl glycidyl ether, phenyl glycidyl ether, the auxiliary includes ammonia, a silane coupling agent, the curing accelerator includes one or both of SH-A100 or 2-ethyl-4-methylimidazole, and the silane coupling agent includes one or both of γ-glycidyl ether propyltrimethoxysilane or γ-aminopropyl triethoxysilane.

[0032] Specifically, the phenolic amine curing agent can cross-link with the base resin such as epoxy resin to form a cured product with excellent performance. In the conductive adhesive, the phenolic amine curing agent can provide strong adhesion and durability, ensuring that the conductive adhesive maintains stable performance in various environments. At the same time, the phenolic amine curing agent has latency and is not easily cross-linked with the base resin such as epoxy resin at room temperature. The curing accelerator can accelerate the curing reaction. Specifically, it can reduce the activation energy of the curing reaction and increase the reaction rate, thereby shortening the curing time of the conductive adhesive. Preferably, SH-A100 is a urea-modified material that does not cure at room temperature and can be stored at room temperature for more than six months, and can be quickly cured at 120-130℃. Preferably, 2-ethyl-4-methylimidazole has little activity at room temperature, but its activity increases significantly as the temperature rises to 130℃, effectively promoting the curing reaction.

[0033] Compared with existing conductive adhesives that slowly cure at room temperature and are difficult to store, the conductive adhesive of the present application is activated for curing at 130 degrees or higher, and completely cured at 160 degrees in 30-60 minutes. Therefore, the conductive adhesive of the present application can be stored for a long time at room temperature and can be cured by reacting at an appropriate temperature during the preparation of the conductive adhesive and during the application of the conductive adhesive.

[0034] Specifically, the butyl glycidyl ether can reduce the viscosity of the epoxy resin, improve the processability, and increase the flowability and operability of the epoxy resin. The phenyl glycidyl ether can improve the flexibility and heat resistance of the cured product. The butyl glycidyl ether and the phenyl glycidyl ether can reduce the viscosity of the conductive adhesive, and the two diluents also have a certain plasticizing effect, which can improve the flexibility and impact resistance of the conductive adhesive.

[0035] Specifically, the ammonia can neutralize the acidic components in the conductive adhesive and adjust the pH value, thereby improving the performance of the conductive adhesive. At the same time, the ammonia also has a certain catalytic effect, which can accelerate the progress of the curing reaction.

[0036] Further, the silane coupling agent can improve the compatibility between the inorganic filler and the organic matrix, and increase the dispersibility and stability of the filler. In the conductive adhesive, the silane coupling agent can enhance the interfacial bonding force between the inorganic filler and the matrix resin, thereby improving the overall performance of the conductive adhesive. Specifically, γ-aminopropyl triethoxysilane has good hydrolytic stability and reactivity, and can form covalent bonds with various substrates (such as metals, glasses, ceramics, etc.), thereby enhancing the interfacial bonding force between the conductive filler and the resin. γ-glycidyloxypropyl trimethoxysilane has an epoxy group, which can react with amine groups or hydroxyl groups in the resin during the curing process to form stable chemical bonds, thereby improving the compatibility and bonding strength of the filler and the resin.

[0037] Further, the preparation method of the synthetic acrylic resin comprises the following steps,

[0038] N1, dissolve the monomers in the solvent in a predetermined ratio, mix well and add to the reaction kettle; weigh the monomers and add to the reaction vessel, stir evenly, add ethyl acetate, continue to stir to dissolve thoroughly. Add a small amount of stabilizer 4-methoxyphenol to prevent polymerization at low temperature, then add the mixed monomer solution to the reaction kettle. The synthesized acrylic resin contains a specific proportion of methyl acrylate, methyl methacrylate, glycidyl methacrylate, styrene and methacrylic acid monomer. Methyl methacrylate can provide hardness and gloss, so that the conductive adhesive has good surface quality after curing. The introduction of glycidyl methacrylate increases the crosslinking property and adhesion of the resin, and helps the stable dispersion of conductive fillers in the resin and the firm combination with the substrate. Styrene improves the rigidity and chemical resistance of the resin, so that the conductive adhesive maintains stable performance in various environments. The use of ethyl acetate as a solvent enables the resin to form a uniform reaction system during synthesis, and in the production of conductive adhesive, ethyl acetate can be used as a good diluent to adjust the viscosity of the conductive adhesive, making it easy to process such as coating, printing or spraying. Compared with ordinary acrylic resins on the market, the synthesized acrylic resin is easier to control viscosity and flowability during processing, and can adapt to different production process requirements.

[0039] N2, drop the initiator into the reaction kettle; heat the reaction kettle to a certain temperature and keep it constant; dissolve the initiator in a small amount of solvent and slowly drop it into the reaction kettle through the dropping device. Heat the reaction kettle to 60-80℃ and keep it constant, continue to stir under constant temperature conditions, and the reaction time is 4-6 hours. The control of reaction conditions ensures that the degree of polymerization and molecular weight distribution of the resin are more uniform, so that it has better rheological properties and processing stability when making conductive adhesive. In the coating process, there is no problem such as sagging, blistering or uneven thickness, which improves the production quality and efficiency of the conductive adhesive.

[0040] N3, after polymerization, the product is cooled, washed and dried. After the reaction is completed, stop heating and let the mixture cool to room temperature naturally. Filter the mixture using a filter device to remove unreacted solid particles. Wash with an appropriate amount of ethyl acetate several times to remove unreacted raw materials and impurities. Dry the washed product in a vacuum drying oven to remove the solvent. The drying temperature is 60-80℃, and the drying time is 12-24 hours until the product is completely dried.

[0041] Further, the preparation method of the phenolic amine curing agent comprises the following steps,

[0042] P1, dissolve dicyandiamide in solvent, mix with formaldehyde, add catalyst, stir evenly; specifically, add dicyandiamide to the reaction container, start stirring after adding ethanol, and make dicyandiamide fully dispersed. Slowly add formaldehyde solution, continue to stir evenly. Add a few drops of hydrochloric acid catalyst, stir evenly.

[0043] P2, gradually add phenol under stirring conditions, maintain the reaction temperature and pH value;

[0044] Slowly add phenol under stirring conditions, control the reaction temperature between 60-80℃, continue to stir. Monitor the pH value of the reaction mixture using a pH meter, and adjust the pH value to pH 7-8 using dilute hydrochloric acid or sodium hydroxide solution, continue to stir the reaction mixture in a neutral or slightly alkaline environment for 2-4 hours until the reaction is completed.

[0045] P3, after the reaction is completed, cool the mixture to room temperature, and cool, wash and dry the product. After the reaction is completed, stop heating and let the mixture cool to room temperature naturally. Filter the mixture using a filter device to remove unreacted solid particles. Wash several times with an appropriate amount of ethanol solvent to remove unreacted raw materials and impurities. Dry the washed product in a vacuum drying oven to remove the solvent. The drying temperature is 60-80℃, and the drying time is 12-24 hours until the product is completely dried.

[0046] Further, another object of the present application is to provide a preparation method of conductive glue, comprising the following steps:

[0047] S1, add part of the diluent, part of the auxiliary agent, and synthetic acrylic resin, epoxy resin, and conductive filler into the double planetary mixer according to the weighed parts, and disperse at high speed until the material is completely dissolved. Put into the reaction kettle with double planetary mixer according to the weighed parts, and stir and disperse at high speed. The purpose of stirring and high-speed dispersion is to make the material completely dissolved to form a uniform solution or suspension. The speed during high-speed dispersion is 400-600 rpm, and the high-speed dispersion time is 30-60 minutes.

[0048] S2, add the latent curing aid, the remaining diluent and the remaining aid, mix uniformly, then vacuum degassing, filter and store in a dry and ventilated environment. First, high-speed dispersion at 400-600 rpm until all materials are added, then high-speed dispersion at 800-1200 rpm, high-speed dispersion time is 3.5-4.5 hours. The addition of latent curing aid can provide longer storage time and better bonding performance. Put the mixed conductive adhesive into the vacuum degassing equipment, vacuum treatment, maintain the vacuum degree at about-0.09 MPa, duration 10-20 minutes, until the bubbles completely disappear, to remove the bubbles generated during mixing, thereby improving the quality of the conductive adhesive. Filter and pack into suitable containers for subsequent use. Store in a dry and ventilated environment at room temperature to ensure the stability and service life of the conductive adhesive.

[0049] Further, another object of the present application is to provide an application of the conductive adhesive, which is applied to a film coating production process.

[0050] As a substitute for lead solder, the conductive adhesive reduces environmental pollution and meets the development trend of green manufacturing. The film coating production process can accurately control the coating thickness and uniformity of the conductive adhesive, ensuring the quality and performance of the product. The electrical connection formed by the conductive adhesive is stable and reliable, which can improve the service life and stability of electronic products. The conductive adhesive can adapt to electronic components of various shapes and sizes, meeting different application scenarios.

[0051] Specifically, the film coating production process includes the following steps:

[0052] Y1: unwinding the carrier film and coating the conductive adhesive;

[0053] Y2: drying and cooling, winding, packaging and finished product delivery.

[0054] Specifically, after the carrier film is coated with the conductive adhesive and dried, in step Y2, the conductive adhesive is dried at 80-100℃ for 30 minutes, the conductive adhesive film layer is 35-45μm thick, and the carrier release film layer is 55-65μm thick.

[0055] Specifically, the conductive component includes a steel sheet layer, a conductive adhesive film layer, a PI insulating layer and a copper foil layer from top to bottom. The conductive adhesive film layer has good peel strength, good high temperature resistance and good conductivity, and through the conductive adhesive film layer, the copper foil layer and the steel sheet layer can realize conduction to complete the shielding effect of the component.

[0056] Specifically, in the production of the conductive component, the conductive adhesive on the carrier release film is connected to the steel sheet by a hot pressing roller with a temperature of 110-140 degrees, a pressure of 4-6 kg, and a speed of 1 minute / meter, the conductive adhesive with the carrier film is connected to the PI surface after the carrier release film is torn off, and the conductive component is fast-pressed and pressed with a temperature of 180±5 degrees, a pre-pressing time of 10 seconds, a forming time of 120-180 seconds, and a pressure of 120±5 kg, and then baked at 160 degrees for 60-90 minutes to stabilize the product.

[0057] The present application has the following advantages over the prior art:

[0058] 1、The present application can reduce the potential possibility of reaction of the acrylic resin and the epoxy resin at room temperature by adding the latent curing aid, thereby improving the storage effect of the conductive adhesive without affecting the use effect, and improving the overall performance of the electronic product and meeting different application scenarios.

[0059] 2、The preparation method of the present application directly mixes the raw materials such as the acrylic resin, the epoxy resin, the conductive filler, the diluent, and the latent curing aid uniformly in the preparation process without separation and storage, thereby reducing the production cost, simplifying the use process of the user, and improving the production efficiency and product quality of the conductive adhesive. DETAILED DESCRIPTION

[0060] In order to make the skilled in the art more clearly understand the technical solutions described in the present application, the following examples are used to illustrate the present application, and the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial channels unless otherwise specified, or can be obtained by known methods.

[0061] The present application will be further described below in conjunction with specific examples:

[0062] A conductive adhesive is made from the following raw materials in parts by weight: synthetic acrylic resin 40-60 parts, epoxy resin 5-15 parts, conductive filler 25-45 parts, latent curing aid 5-15 parts, diluent 80-120 parts, and aid 5-8 parts.

[0063] Further, the epoxy resin includes a trifunctional alicyclic epoxy resin and a bisphenol A epoxy resin.

[0064] The ratio of the trifunctional alicyclic epoxy resin and the bisphenol A epoxy resin of the epoxy resin is 3:7-5:5.

[0065] The conductive filler includes at least two or more of silver-coated polystyrene microspheres, modified carbon nanotubes, flaky silver powder, and modified expanded graphite. The modified carbon nanotubes are carboxylated carbon nanotubes. The modified expanded graphite is a material after ZIF-7 is compounded with expanded graphite.

[0066] Further, the latent curing aid includes one or more of a phenolic amine curing agent, a curing accelerator, the diluent includes one or more of butyl glycidyl ether, phenyl glycidyl ether, the aid includes ammonia, a silane coupling agent, the curing accelerator includes one or both of SH-A100 or 2-ethyl-4-methylimidazole, the SH-A100 is purchased from Guangzhou Xinxin Metallurgical Chemical Co., Ltd., and the silane coupling agent includes one or both of gamma-glycidoxypropyltrimethoxysilane or gamma-aminopropyltriethoxysilane.

[0067] A method for preparing modified carbon nanotubes, comprising the following steps:

[0068] P1, 100ml of concentrated nitric acid and 300ml of concentrated sulfuric acid are configured according to a volume ratio of 1:3 to form a mixed acid solution, 2g of multi-walled carbon nanotubes are slowly added to the mixed acid solution and stirred constantly at the same time;

[0069] P2, ultrasonic treatment is performed at 50°C for 4 hours, after the ultrasonic treatment is completed, heating and stirring are performed, and reflux reaction is performed at 50°C for 3 hours to obtain a reaction liquid;

[0070] P3, the reaction liquid is slowly poured into a container containing 1L of deionized water, and then filtered, washed with a large amount of deionized water until the pH approaches 7, and the acidified carbon nanotubes are vacuum dried at 80°C for 12 hours to obtain carboxylated carbon nanotubes.

[0071] Specifically, the method for preparing the modified expanded graphite is:

[0072] Q1, 0.6g of zinc nitrate hexahydrate and 1.5g of 2-methylimidazole are respectively dissolved in 30ml

[0073] of methanol and mixed, stirred vigorously for 2 hours and then allowed to stand for 24 hours to allow the crystals to grow fully, centrifuged, washed with anhydrous methanol 3 times, and white powder is obtained, and the ZIF-7 crystals are vacuum dried at 50°C for 12 hours;

[0074] Q2, 10g of natural flake graphite is added to 200ml of concentrated sulfuric acid, stirred uniformly, 10g of sodium nitrate is slowly added, stirring is continued, and 20g of potassium permanganate is added in three times, the temperature is controlled between 25°C to avoid violent reaction. After 4 hours of reaction, deionized water is added for dilution, and then hydrogen peroxide is added to stop the reaction; after washing and drying, it is placed in a high-temperature furnace, heated rapidly at 800-1000°C, expanded, and cooled to obtain expanded graphite.

[0075] Q3, 1g of ZIF-7 and 1g of expanded graphite were added to 30ml of ethanol, 0.1g of polyvinylpyrrolidone and 0.1g of 3-aminopropyl triethoxysilane were added, and stirring was continued for 1 hour, the mixture was placed in an ultrasonic cleaner and ultrasonic treatment was carried out for 30 minutes;

[0076] Q4, the mixture after ultrasonic treatment was filtered, the solid part was collected, washed with ethanol and vacuum dried at 60°C for 12 hours.

[0077] The preparation method of the synthetic acrylic resin comprises the following steps:

[0078] N1, according to the weight fraction, 40 parts of methyl acrylate, 10 parts of methyl methacrylate, 30 parts of glycidyl methacrylate, 15 parts of styrene and 5 parts of methyl methacrylate monomer were dissolved in 300 parts of ethyl acetate solvent, 0.5 parts of stabilizer 4-methoxy phenol was added, and the mixture was uniformly added to the reaction kettle.

[0079] N2, 0.5 parts of dibenzoyl peroxide was added dropwise to the reaction kettle; the reaction kettle was heated to 80°C and kept constant, and the stirring was continued under constant temperature condition, and the reaction time was 6 hours.

[0080] N3, after the reaction was completed, the heating was stopped, and the mixture was naturally cooled to room temperature. The mixture was filtered using a filtering device to remove the unreacted solid particles. It was washed with an appropriate amount of ethyl acetate for 3 times to remove the unreacted raw materials and impurities. The washed product was dried in a vacuum drying oven to remove the solvent. The drying temperature was 80°C, and the drying time was 24 hours until the product was completely dried.

[0081] The preparation method of the phenolic amine curing agent comprises the following steps:

[0082] P1, 100g of dicyandiamide was stirred and dissolved in 200g of ethanol, 50g of 37% formaldehyde aqueous solution was slowly added, and stirring was continued until uniform. A few drops of hydrochloric acid catalyst were added and stirred uniformly.

[0083] P2, under stirring condition, 80g of phenol was gradually added, the reaction temperature was controlled at 80°C, and the pH value was adjusted to pH 7 with dilute hydrochloric acid or sodium hydroxide solution, and the reaction mixture was continuously stirred for 4 hours under neutral environment until the reaction was completed.

[0084] P3, after the reaction was completed, the heating was stopped, and the mixture was naturally cooled to room temperature. The mixture was filtered using a filtering device to remove the unreacted solid particles. It was washed with an appropriate amount of ethanol solvent for 3 times to remove the unreacted raw materials and impurities. The washed product was dried in a vacuum drying oven to remove the solvent. The drying temperature was 80°C, and the drying time was 24 hours until the product was completely dried.

[0085] The preparation method of the conductive adhesive comprises the following steps:

[0086] S1, add synthetic acrylic resin, epoxy resin, conductive filler, and part of the auxiliary agent into part of the diluent, put them into the double planetary mixer according to the weighed parts, and disperse at high speed until all the materials are dissolved. The rotation speed is 400-600 rpm during high-speed dispersion, and the high-speed dispersion time is 30-60 minutes.

[0087] S2, add the latent curing aid, the remaining diluent and the remaining auxiliary agent, mix uniformly, first disperse at a speed of 400-600 rpm until all the materials are added, then disperse at a speed of 800-1200 rpm, and disperse for 3.5-4.5 hours. Put the mixed conductive adhesive into a vacuum degassing device, perform vacuum treatment, maintain the vacuum degree at about-0.09 MPa, and continue for 20 minutes until the bubbles disappear completely, to remove the bubbles generated during the mixing process. Filter and package the conductive adhesive and store it in a dry and ventilated environment at room temperature.

[0088] The film production process comprises the following steps:

[0089] Y1: unwinding the carrier film, and coating the conductive adhesive;

[0090] Y2: drying and cooling, winding, packaging, and finished product delivery.

[0091] After coating the conductive adhesive on the carrier film and drying, in step Y2, the conductive adhesive is dried at 100°C for 30 minutes, the conductive adhesive film layer is 40 μm thick, and the carrier release film layer is 60 μm thick.

[0092] The conductive component comprises a steel sheet layer, a conductive adhesive film layer, a PI insulation layer, and a copper foil layer from top to bottom. The conductive adhesive on the carrier release film is connected to the steel sheet through a hot press roller with a temperature of 130 degrees, a pressure of 5 kg, and a speed of 1 minute / meter. The conductive adhesive with the carrier film is adhered to the PI surface after tearing off the carrier release film, and the conductive component is pressed at a temperature of 180 degrees, a pre-pressing time of 10 seconds, a forming time of 150 seconds, and a pressure of 120 kg. After pressing, the product is baked at 160 degrees for 70 minutes to stabilize the product.

[0093] Table 1: weight component ratio of the formula

[0094]

[0095] Example 1

[0096] The preparation method of the conductive adhesive comprises the following steps:

[0097] S1, add synthetic acrylic resin, epoxy resin, conductive filler, silane coupling agent into 60 parts of butyl glycidyl ether, put into double planetary mixer according to the weighed parts, high speed dispersion until all the materials are dissolved. The speed is 400 rpm during high speed dispersion, and the high speed dispersion time is 30 minutes.

[0098] S2, add latent curing aid, remaining diluent and remaining aid, mix uniformly, first high speed dispersion at 400 rpm until all materials are added, then high speed dispersion at 800 rpm, high speed dispersion for 3.5 hours. Put the mixed conductive adhesive into vacuum degassing equipment, perform vacuum treatment, keep the vacuum degree at about-0.09 MPa, for 20 minutes until the bubbles disappear completely, to remove the bubbles generated during mixing, filter and pack the conductive adhesive into suitable containers. Store in a dry and ventilated environment at room temperature.

[0099] Example 2

[0100] The preparation method of the conductive adhesive comprises the following steps:

[0101] S1, add synthetic acrylic resin, epoxy resin, conductive filler, silane coupling agent into 80 parts of butyl glycidyl ether, put into double planetary mixer according to the weighed parts, high speed dispersion until all the materials are dissolved. The speed is 600 rpm during high speed dispersion, and the high speed dispersion time is 60 minutes.

[0102] S2, add latent curing aid, remaining diluent and remaining aid, mix uniformly, first high speed dispersion at 600 rpm until all materials are added, then high speed dispersion at 1200 rpm, high speed dispersion for 4.5 hours. Put the mixed conductive adhesive into vacuum degassing equipment, perform vacuum treatment, keep the vacuum degree at about-0.09 MPa, for 20 minutes until the bubbles disappear completely, to remove the bubbles generated during mixing, filter and pack the conductive adhesive into suitable containers. Store in a dry and ventilated environment at room temperature.

[0103] Example 3

[0104] The preparation method of the conductive adhesive comprises the following steps:

[0105] S1, add synthetic acrylic resin, epoxy resin, conductive filler, silane coupling agent into 50 parts of butyl glycidyl ether, put into double planetary mixer according to the weighed parts, high speed dispersion until all the materials are dissolved. The speed is 500 rpm during high speed dispersion, and the high speed dispersion time is 50 minutes.

[0106] S2, add the latent curing co-agent, the remaining diluent and the remaining co-agent, mix uniformly, first carry out high-speed dispersion at 450 rpm until all the materials are added, then use high-speed dispersion at a speed of 900 rpm, high-speed dispersion for 3.5 hours. Put the mixed conductive adhesive into the vacuum degassing equipment, carry out vacuum treatment, keep the vacuum degree at about -0.09 MPa, the duration is 20 minutes, until the bubbles completely disappear, to remove the bubbles generated in the mixing process, filter and pack the conductive adhesive into the appropriate container. Store in a dry and ventilated environment at room temperature.

[0107] Example 4

[0108] The preparation method of the conductive adhesive comprises the following steps:

[0109] S1, add the synthetic acrylic resin, epoxy resin, conductive filler and silane coupling agent into 50 parts of butyl glycidyl ether, put them into the double planetary mixer according to the weighed parts, high-speed dispersion until all the materials are dissolved. The speed is 4500 rpm during high-speed dispersion, and the high-speed dispersion time is 45 minutes.

[0110] S2, add the latent curing co-agent, the remaining diluent and the remaining co-agent, mix uniformly, first carry out high-speed dispersion at 450 rpm until all the materials are added, then use high-speed dispersion at a speed of 900 rpm, high-speed dispersion for 3.5 hours. Put the mixed conductive adhesive into the vacuum degassing equipment, carry out vacuum treatment, keep the vacuum degree at about -0.09 MPa, the duration is 20 minutes, until the bubbles completely disappear, to remove the bubbles generated in the mixing process, filter and pack the conductive adhesive into the appropriate container. Store in a dry and ventilated environment at room temperature.

[0111] Example 5

[0112] The preparation method of the conductive adhesive comprises the following steps:

[0113] S1, add the synthetic acrylic resin, epoxy resin, conductive filler and silane coupling agent into 50 parts of butyl glycidyl ether, put them into the double planetary mixer according to the weighed parts, high-speed dispersion until all the materials are dissolved. The speed is 4500 rpm during high-speed dispersion, and the high-speed dispersion time is 45 minutes.

[0114] S2, add the latent curing co-agent, the rest of the diluent and the rest of the co-agent, mix well, first carry out high speed dispersion at 550 rpm until all materials are added, then use high speed dispersion at 1100 rpm, high speed dispersion for 4.5 hours. Put the mixed conductive adhesive into the vacuum defoaming equipment, carry out vacuum treatment, keep the vacuum degree at about -0.09 MPa, the duration is 20 minutes, until the bubbles completely disappear, to remove the bubbles generated in the mixing process, filter and pack the conductive adhesive into the appropriate container. Store in a dry and ventilated environment at room temperature.

[0115] Comparative Example 1

[0116] The main difference between Comparative Example 1 and Example 2 is that Comparative Example 1 uses a commercially available acrylic resin instead of synthesizing the acrylic resin. The remaining steps and component parameters of Comparative Example 1 are the same as Example 2.

[0117] Comparative Example 2

[0118] The main difference between Comparative Example 2 and Example 2 is that Comparative Example 2 uses a commercially available epoxy resin E44 instead of the epoxy resin. The remaining steps and component parameters of Comparative Example 2 are the same as Example 2.

[0119] Comparative Example 3

[0120] The main difference between Comparative Example 3 and Example 2 is that Comparative Example 3 uses silver-coated polystyrene microspheres with an addition ratio of 70% and 30% of granular silver powder instead of the conductive filler. The remaining steps and component parameters of Comparative Example 3 are the same as Example 2.

[0121] Comparative Example 4

[0122] The main difference between Comparative Example 4 and Example 2 is that Comparative Example 4 uses a commercially available curing agent instead of the phenolic amine curing agent. The remaining steps and component parameters of Comparative Example 4 are the same as Example 2.

[0123] Comparative Example 5

[0124] The main difference between Comparative Example 5 and Example 2 is that Comparative Example 5 omits the curing accelerator and does not add the curing accelerator in the conductive adhesive preparation step. The remaining steps and component parameters of Comparative Example 5 are the same as Example 2.

[0125] The above examples and comparative examples were tested for performance, wherein the thickness before and after compression was tested using a micrometer; the 90 degree peel strength was tested using test method IPC-TM-650-2.4.9, the solder heat resistance test method was IPC-TM-650-2.4.13, the transferability test method was a press machine, and for the grounding resistance (grounding hole Ф1.00mm), the test method after curing was an ohmmeter, the test method for SMT3 was a reflow soldering furnace, an ohmmeter, 85°C, 85%RH, 96H was a high temperature and high humidity chamber, and an ohmmeter. The test data are shown in Tables 2 and 3:

[0126] Table 2: Performance test results of examples 1-5

[0127]

[0128] Table 3: Performance test results of comparative examples 1-5

[0129]

[0130] As shown in Table 2, by adding the latent curing aid in examples 1-5, the reactivity of the acrylic resin and the epoxy resin at room temperature can be reduced, thereby improving the storage effect of the conductive adhesive, while not affecting its performance. In the test items in Table 2, the thickness change of examples 1-5 after compression is not large, the solder heat resistance is good, the transferability at 130°C is good, and the conductive ability is good. The conductive adhesive prepared in examples 1-5 can improve the overall performance of electronic products and meet different application scenarios. The preparation method of examples 1-5 directly mixes the raw materials such as acrylic resin, epoxy resin, conductive filler, additive, diluent and latent curing aid uniformly in the preparation process, without the need for separation and storage, thereby reducing production costs, simplifying the user's use process, and improving the production efficiency and product quality of the conductive adhesive.

[0131] As shown in Table 3, comparative example 1 uses a commercially available ordinary acrylic resin, while example 2 uses a synthetic acrylic resin prepared for the conductive adhesive. By adjusting the ratio of monomers, the synthetic acrylic resin has better heat resistance, crosslinking density, and polar groups combined with other resins and fillers, so that the peel strength, heat resistance and conductive performance of example 2 are better than those of comparative example 1.

[0132] Comparative example 2 uses a commercially available ordinary epoxy resin, while example 2 uses an epoxy resin containing a trifunctional alicyclic epoxy resin with higher heat resistance and higher crosslinking density. The conductive adhesive after crosslinking reaction has better mechanical properties, weather resistance and electrical properties, so that the peel strength, heat resistance and conductive performance of example 2 are better than those of comparative example 2.

[0133] Compared with Example 2, the silver-coated polystyrene microspheres and the particulate silver powder are used in Comparative Example 3, and the silver-coated polystyrene microspheres, modified carbon nanotubes, silver powder and modified expanded graphite are used in Example 2. The electrical properties of the conductive adhesive can be improved, and the cost can be reduced. Since the conductive fillers in Example 2 have a larger specific surface area than those in Comparative Example 3, the thickness change of the conductive adhesive after compression is small, the conductive adhesive does not become locally uneven, the mechanical properties of the conductive adhesive are improved, and the peel strength, heat resistance and electrical conductivity of Example 2 are all better than those of Comparative Example 3.

[0134] Compared with Example 2, the commercially available curing agent is used in Comparative Example 4. Since the commercially available curing agent lacks latency, the curing activity of the conductive adhesive is low, and during storage, the system is unstable due to the premature reaction of some materials, the delamination between the diluent and the resin, and the precipitation of some conductive filler components. Finally, during the preparation of the conductive adhesive, the peel strength, heat resistance and electrical conductivity of Comparative Example 4 do not have advantages compared with the other comparative examples and examples.

[0135] Compared with Example 2, the curing accelerator is omitted in Comparative Example 5, which results in the need for more curing activity to trigger the reaction between the curing agent and the resin. Since the application of the present application is to cure under specific temperature conditions, the curing degree of the conductive adhesive of Comparative Example 5 will be poorer than that of Example 2. The peel strength, heat resistance and electrical conductivity of Comparative Example 5 are also poorer than those of Example 2.

[0136] The above is a preferred embodiment of the present application. Those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. An electrically conductive adhesive, characterized in that, The synthetic acrylic resin is prepared by using the following raw materials: 40-60 parts of synthetic acrylic resin, 5-15 parts of epoxy resin, 25-45 parts of conductive filler, 5-15 parts of latent curing aid, 80-120 parts of diluent, and 5-8 parts of auxiliary agent; The synthetic acrylic resin is prepared by using the following raw materials: 40-60 parts of synthetic acrylic resin, 5-15 parts of epoxy resin, 25-45 parts of conductive filler, 5-15 parts of latent curing aid, 80-120 parts of diluent, and 5-8 parts of auxiliary agent; The synthetic acrylic resin is prepared by using the following raw materials: 40-60 parts of synthetic acrylic resin, 5-15 parts of epoxy resin, 25-45 parts of conductive filler, 5-15 parts of latent curing aid, 80-120 parts of diluent, and 5-8 parts of auxiliary agent; The conductive filler includes at least one or more of modified carbon nanotubes and silver-coated polystyrene microspheres, silver powder, and modified expanded graphite; the modified carbon nanotubes are carboxylated carbon nanotubes; and the modified expanded graphite is a material obtained by compounding ZIF-7 and expanded graphite. The latent curing aid includes phenolic amine curing agent and curing accelerator, and the curing accelerator includes one or both of SH-A100 and 2-ethyl-4-methylimidazole. The preparation method of the synthetic acrylic resin includes the following steps: N1, 40 parts of methyl acrylate, 10 parts of methyl methacrylate, 30 parts of glycidyl methacrylate, 15 parts of styrene, and 5 parts of methacrylic acid monomer are dissolved in 300 parts of ethyl acetate solvent according to the weight fraction, 0.5 parts of stabilizer 4-methoxyphenol is added, and the mixture is uniformly mixed and added to a reaction kettle; N2, 0.5 parts of dibenzoyl peroxide is added dropwise to the reaction kettle; the reaction kettle is heated to 80℃ and kept at constant temperature, and continuous stirring is carried out under constant temperature conditions, and the reaction time is 6 hours; N3, after the polymerization is completed, the product is cooled to room temperature, washed with ethyl acetate, and dried, and the drying temperature is 80℃ and the drying time is 24 hours; The preparation method of the phenolic amine curing agent includes the following steps: P1, 100g of dicyandiamide is stirred and dissolved in 200g of ethanol, 50g of 37% formaldehyde aqueous solution is slowly added, a hydrochloric acid catalyst is added, and stirring is uniformly carried out; P2, under stirring conditions, 80g of phenol is gradually added, the reaction temperature is maintained at 80℃, the pH value is adjusted to 7, and the reaction mixture is continuously stirred for 4 hours under neutral environment until the reaction is completed; P3, after the reaction is completed, the mixture is cooled to room temperature, the product is cooled, washed with ethanol, and dried, and the drying temperature is 80℃ and the drying time is 24 hours.

2. The electrically conductive adhesive of claim 1, wherein: The diluent includes one or more of butyl glycidyl ether and phenyl glycidyl ether, and the auxiliary agent includes ammonia and silane coupling agent, and the silane coupling agent includes one or both of γ-glycidyl ether propyl trimethoxysilane and γ-aminopropyl triethoxysilane.

3. The electrically conductive adhesive of claim 1, wherein: The ratio of the trifunctional alicyclic epoxy resin and the bisphenol A epoxy resin of the epoxy resin is 3:7-5:5 according to the weight fraction.

4. A method for preparing a conductive adhesive comprising the conductive adhesive according to any one of claims 1 to 3, characterized in that, The method includes the following steps: S1, the synthetic acrylic resin, epoxy resin, conductive filler, and part of the auxiliary agent are added to part of the diluent, and are put into a double-planetary stirrer according to the weighed fraction, and are high-speed dispersed until the materials are completely dissolved; the rotation speed is 400-600 revolutions / minute during high-speed dispersion, and the high-speed dispersion time is 30-60 minutes; S2, add the latent curing co-agent, the remaining diluent and the remaining co-agent, mix uniformly, first carry out high-speed dispersion at 400-600 rpm until all materials are added, then use high-speed dispersion at 800-1200 rpm, high-speed dispersion for 3.5-4.5 hours, then vacuum degassing, maintain the vacuum degree at -0.09 MPa, duration 20 minutes until the bubbles completely disappear, filter and pack, store at room temperature in a dry and ventilated environment.

5. Use of a conductive adhesive comprising the conductive adhesive according to any one of claims 1 to 3, characterized in that The conductive adhesive is applied to a film production process. The film production process comprises the following steps, Y1: unwinding of the carrier film, coating of the conductive adhesive; Y2: drying and cooling, winding, packaging, and finished product delivery; In step Y2, the conductive adhesive is dried at 80-100°C for 30 minutes, the conductive adhesive film layer is 35-45 μm thick, and the carrier release film layer is 55-65 μm thick.

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