Epoxy resin packaging bonding material with high bonding stability and preparation method thereof

Abstract

The invention provides an epoxy resin packaging bonding material with high bonding stability and a preparation method thereof. The packaging bonding material is prepared from the following raw material components: 8 to 18 percent of graphene oxide modified epoxy resin, 0.8 to 4.0 percent of a curing agent, 0 to 1 percent of a curing accelerator, 0.4 to 2.0 percent of a silane coupling agent, 2 to 7 percent of nano carbon black, 2 to 7 percent of carbon fiber, 40 to 60 percent of flaky silver powder, 4 to 8 percent of spherical silver powder, 4.4 to 13.6 percent of a surface treating agent, 4 to 6 percent of a reactive diluent, 0.5 to 1.5 percent of a toughening agent, 0.5 to 1.5 percent of a dispersing agent, 0.1 to 0.5 percent of a lubricating agent and the balance of a non-reactive diluent. Graphene oxide is utilized to modify epoxy resin, the dispersion stability of the filler is improved, modified carbon black is adopted as a short-range conductive additive, carbon fibers are adopted as a long-range conductive additive, the modified carbon black and the carbon fibers synergistically improve the conductivity, and the reinforcing effect is achieved. The packaging bonding material disclosed by the invention has the characteristics of low volume resistivity, high tensile strength and bending strength, high bonding stability and the like, and has wide application prospects in the fields of automotive electronics, wind power photovoltaics, LEDs (Light Emitting Diode), LCDs (Liquid Crystal Display) and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive adhesives, and in particular to an epoxy resin encapsulation adhesive material with high bonding stability and a preparation method thereof. Background Art

[0002] Traditional Pb / Sn solder is widely used due to its excellent performance and low cost, but it can cause irreversible damage to both the environment and the human body. While lead-free solder offers no environmental pollution concerns, its high melting point prevents it from being used on substrates or wires that are sensitive to high temperatures, limiting its application in electronic packaging, particularly smart packaging. Currently, the most promising material to replace solder is conductive adhesive. As a solder alternative, conductive adhesive is an adhesive that combines electrical conductivity and bonding capabilities. Its advantages include being lead-free, offering a small bond gap, a low curing temperature, high resolution, and wide adaptability. It holds broad application prospects in areas such as microelectronics assembly, IC packaging, and LED packaging.

[0003] With the development of the electronics industry, the size of electronic components continues to shrink, and the integration of electronic products continues to increase. The internal stress, adhesion, thermal conductivity, electrical properties, etc. of electronic device packaging connection materials are facing more stringent requirements. The survey found that due to the widespread shortage of key raw materials, low advanced formulations, and backward packaging technology in the industry, domestic conductive adhesive materials generally have customer pain points such as poor conductivity, low bonding stability, and high product costs. The mechanical properties of conductive adhesives are also an important factor affecting bonding stability. Conductive adhesives with poor mechanical properties will easily damage the conductive adhesive body, resulting in poor bonding stability. The volume resistivity of conductive adhesives currently on the market is 5.0×10 -4 The average strength of epoxy conductive silver adhesive is approximately 0.1 Ω·cm (tested in accordance with GB / T1692-2008), the flexural strength does not exceed 80 MPa (tested in accordance with GB / T2567-2008), and the tensile strength does not exceed 35 MPa (tested in accordance with GB / T2567-2008). Meanwhile, the production cost of epoxy conductive silver adhesive remains high, primarily due to the high price of silver powder, the conductive phase, which accounts for 80-90% of the adhesive's production cost. Therefore, how to reduce the silver powder content in epoxy conductive silver adhesive while ensuring high conductivity and high bonding stability has become a focus of ongoing industry attention.

[0004] The invention patent application CN113930216A discloses a method for preparing a low-silver-filled conductive adhesive, comprising the following steps: 1) heat-treating the conductive filler flaky silver powder; 2) adding the heat-treated silver powder to a surface modifier solution for surface modification, dispersion, ultrasonication, filtration, washing, and drying to obtain surface-modified silver powder; 3) using an organic silicone resin as the base resin, adding additives and mixing and dispersing them uniformly, then adding the surface-modified silver powder and mixing uniformly to obtain a conductive adhesive with a silver powder filling of 55% to 65%. The conductive adhesive prepared by this method has a volume resistivity of 2.5-3.5%.

[0005] 6.8×10 -4 ~1.2×10 -3 Ω·cm, poor electrical conductivity.

[0006] There is a patented method for preparing a low-silver content epoxy conductive adhesive (application publication number: CN117050701A). This method optimizes the epoxy value and viscosity of the epoxy resin to balance the curing shrinkage during the curing process and the epoxy resin's wettability to silver powder. The silver powder is then heat-treated; the silver powder accounts for 50-65% of the conductive adhesive product by mass. This low-silver content epoxy conductive adhesive can still maintain high conductivity, with a volume resistivity of less than 10 -4 Ω·cm, but the patent does not address the bonding stability of the conductive adhesive.

[0007] Patent application publication number CN118685139A discloses a nano-silver, highly thermally conductive conductive adhesive for chip applications and its preparation method. This conductive adhesive, made from 70-90% silver powder and 3-15% epoxy resin, is used in chip packaging and exhibits excellent long-term thermal stability and reliability. However, the silver powder mass ratio in this conductive adhesive is as high as 70-90%, making the material cost significantly uncompetitive.

[0008] In summary, the conductive adhesive prepared by existing technology is difficult to simultaneously meet the requirements of low silver powder content, low volume resistivity and high bonding stability. The research and development of conductive adhesives with high bonding stability, high thermal conductivity and low silver powder content has become a hot topic in current research. Summary of the Invention

[0009] In view of the deficiencies in the prior art, the object of the present invention is to provide an epoxy resin encapsulation adhesive material with high bonding stability, which has excellent thermal conductivity, electrical conductivity and mechanical properties, improves bonding stability, and has cost advantages.

[0010] Another object of the present invention is to provide a method for preparing the epoxy resin encapsulation adhesive material with high bonding stability.

[0011] To achieve the purpose of the present invention, the present invention provides an epoxy resin encapsulation adhesive material with high bonding stability, which comprises the following raw material components by weight percentage: 10-16% of graphene oxide modified epoxy resin, 0.8-4.0% of curing agent, 0-1% of curing accelerator, 0.4-2.0% of silane coupling agent, 2-7% of nano carbon black, 2-7% of carbon fiber, 40-60% of flaky silver powder, 4-8% of spherical silver powder, 4.4-13.6% of surface treatment agent, 4-6% of active diluent, 0.5-1.5% of toughening agent, 0.5-1.5% of dispersant, 0.1-0.5% of lubricant, and the balance of inactive diluent.

[0012] Graphene oxide-modified epoxy resin is a modified epoxy resin obtained by doping graphene oxide into epoxy resin. Graphene oxide, the product of graphene oxidation, is a novel carbon material with excellent performance. It has a large specific surface area and is rich in oxygen-containing functional groups on its surface. These functional groups make graphene oxide more easily bonded with polymers, effectively improving the interaction between graphene oxide and polymers. Graphene oxide has a physical structure and properties similar to those of graphene. Using it as an admixture for epoxy resin modification can not only enhance the dispersion stability of graphene oxide fillers and prevent graphene particle agglomeration, but also improve the electrical and thermal conductivity of composite conductive connection materials and enhance the mechanical strength of encapsulating adhesive materials.

[0013] The present invention adopts modified nano carbon black as a short-range conductive additive and carbon fiber as a long-range conductive additive, utilizes the synergistic effect between carbon black and carbon fiber, improves the conductivity of carbon-carbon composite conductive filler, and has an enhancement effect.

[0014] The silver powder used in the present invention is a compound of spherical silver powder and flaky silver powder. Flake silver powder forms a low-resistance path through surface contact or line contact. Its specific surface area is large and its arrangement is more conducive to electron transfer. At the same mass, its volume resistivity is lower than that of spherical silver powder; spherical silver powder can fill the gaps between the flaky silver powders, so that adjacent silver sheets that were originally not in contact form parallel conductive paths, further reducing the overall contact resistance. At the same time, the flaky silver powder provides a base conductive network, and the spherical silver powder enhances the electron transmission efficiency in three-dimensional space. The combination of the two forms a denser conductive path. In addition, the compound system of spherical silver powder and flaky silver powder can reduce the total amount of silver powder while ensuring performance and reduce material costs by optimizing the conductive network structure. Therefore, the compound of flake and spherical silver powders achieves a synergistic improvement in conductivity, processability and economy through geometric complementarity and conductive path optimization.

[0015] In some embodiments of the present invention, the high bonding stability epoxy resin encapsulation adhesive material includes the following raw material components by weight percentage: 8-18% graphene oxide modified epoxy resin, 1.8-3% curing agent, 0-1% curing accelerator, 0.4-2.0% silane coupling agent, 3-6% nano carbon black, 3-6% carbon fiber, 48-52% flaky silver powder, 4-8% spherical silver powder, 5-7.3% surface treatment agent, 5-6% active diluent, 0.5-1.5% toughening agent, 0.5-1.5% dispersant, 0.1-0.5% lubricant, and 2-10% inactive diluent.

[0016] In some embodiments of the present invention, the graphene oxide-modified epoxy resin is prepared by the following steps: Step 1: stirring and mixing graphite powder, concentrated sulfuric acid and phosphoric acid, then slowly adding KMnO4 and H2O2, washing until neutral, and finally drying to obtain graphene oxide; Step 2: preheating the epoxy resin in a water bath to make it a flowable liquid, and at the same time adding graphene oxide to anhydrous ethanol to uniformly disperse the graphene oxide in the anhydrous ethanol; then pouring the anhydrous ethanol solution of graphene oxide into the epoxy resin, after sufficient dispersion, stirring in a water bath, and then vacuuming to degas and evaporate the anhydrous ethanol.

[0017] In some embodiments of the present invention, in step 1, stirring and mixing the graphite powder, concentrated sulfuric acid, and phosphoric acid is carried out in an ice-water bath, washing to neutrality is carried out using a 3% hydrochloric acid solution and deionized water, and drying is carried out by freeze-drying; the graphene oxide has a purity greater than 97 wt%, a diameter between 3 and 10 μm, a number of layers less than 5, and a thickness of 0.55 to 2.0 nm.

[0018] In some embodiments of the present invention, in step 2, the epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and alicyclic epoxy resin; the bisphenol A epoxy resin is at least one of E-51, E-55, E-35, E-42, and E-44; the bisphenol F epoxy resin is at least one of NPEF-170 and DER354; the alicyclic epoxy resin is at least one of S-06E, TT21, and EP-4221-A; the weight percentage of the graphene oxide in the epoxy resin is 0.1-1.0%; the temperature of the water bath is 50-70°C, and the graphene oxide is uniformly dispersed in anhydrous ethanol by ultrasonic dispersion, and the anhydrous ethanol solution of graphene oxide and the epoxy resin are fully dispersed; the stirring time in the water bath is 20-40 minutes, and the vacuum degassing is carried out in a vacuum box at 70-90°C and maintained for 1-2 hours.

[0019] In some embodiments of the present invention, the nano carbon black is modified by the silane coupling agent.

[0020] In some embodiments of the present invention, the nano-carbon black and the inactive diluent are dispersed using high-frequency vibration ultrasound, and then modified with the silane coupling agent; wherein the weight ratio of the nano-carbon black to the inactive diluent used to disperse the nano-carbon black is 10:1 to 5:1, and the silane coupling agent is 2.0 to 6.0% by weight of the nano-carbon black. The nano-carbon black treated in the above steps can ensure uniform dispersion of the nano-carbon black and enhance the interfacial bonding strength between the carbon black and the base resin.

[0021] In some embodiments of the present invention, the particle size of the nano carbon black is 20 to 80 nm.

[0022] In some embodiments of the present invention, the carbon fiber has an aspect ratio of 100 to 500 and a diameter of 50 to 200 nm;

[0023] In some embodiments of the present invention, the weight ratio of the carbon fiber to the nano carbon black is 4:1 to 1:4, preferably 2:1 to 1:2.

[0024] In some embodiments of the present invention, the spherical silver powder and the flake silver powder are compounded in a mass ratio of 1:(5.0-15.0).

[0025] In some embodiments of the present invention, the average particle size of the flaky silver powder is 2 to 6 μm, and the tap density is 3.8 to 5.6 g / cm 3 .

[0026] In some embodiments of the present invention, the average particle size of the spherical silver powder is 0.2-0.5 μm, and the tap density is 3.0-4.8 g / cm 3 .

[0027] In some embodiments of the present invention, the spherical silver powder and the flaky silver powder are pre-treated with a surface treatment agent for coating. Chemically coating the silver powder surface with the surface treatment agent to form a spatial isolation layer effectively reduces agglomeration between silver powder particles and delays oxidation, thereby improving their dispersibility and other properties.

[0028] In some embodiments of the present invention, the surface treatment agent is stearic acid. Stearic acid molecules bind to the silver surface through carboxyl groups, and its long-chain alkyl groups provide an anti-aggregation effect, which can better reduce the agglomeration of silver powder particles and delay oxidation.

[0029] In some embodiments of the present invention, the weight ratio of the total mass of the spherical silver powder and the flaky silver powder to the surface treatment agent is 1:(0.10-0.15).

[0030] In some embodiments of the present invention, the curing agent is at least one of an aromatic amine curing agent, an aliphatic amine curing agent, a polyamide curing agent, and an acid anhydride curing agent.

[0031] In some embodiments of the present invention, the curing accelerator is at least one of 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole.

[0032] In some embodiments of the present invention, the silane coupling agent is at least one of vinyltriethylsilane, γ-aminopropyltrimethylsilane, γ-aminopropyltriethylsilane, 3-methacryloxypropyltrimethoxysilane and hexamethylenediaminomethyltrimethoxysilane.

[0033] In some embodiments of the present invention, the reactive diluent is at least one of tert-butylphenyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, trimethylolethane triglycidyl ether, ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, and o-cresyl glycidyl ether.

[0034] In some embodiments of the present invention, the inactive diluent is at least one of propylene glycol methyl ether acetate, ethylene glycol ethyl ether, ethyl propionate, isobutyl formate, methyl propionate, butyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, n-butanol, and acetone.

[0035] In some embodiments of the present invention, the toughening agent is at least one of carboxyl-terminated nitrile rubber, core-shell toughening agent, and polysulfide rubber.

[0036] In some embodiments of the present invention, the dispersant is at least one of polyvinyl alcohol, sodium pyrophosphate, and sodium hexametaphosphate.

[0037] In some embodiments of the present invention, the lubricant is at least one of EBS, stearic acid, lauric acid, stearamide, and oleamide.

[0038] To achieve another object of the present invention, the present invention provides a method for preparing the epoxy resin encapsulation adhesive material with high bonding stability as described in any of the above schemes, comprising the following steps:

[0039] S1. Preparation of graphene oxide modified epoxy resin: Graphite powder, concentrated sulfuric acid and phosphoric acid are stirred and mixed, and then KMnO4 and H2O2 are slowly added, followed by washing until neutrality, and finally drying to obtain graphene oxide; the epoxy resin is preheated in a water bath to make it a flowable liquid, and the graphene oxide is added to anhydrous ethanol to uniformly disperse the graphene oxide in the anhydrous ethanol; the anhydrous ethanol solution of graphene oxide is then poured into the epoxy resin, and after being fully dispersed, the mixture is stirred in a water bath, and then vacuumed to degas and evaporate the anhydrous ethanol;

[0040] S2. Preparing a silane coupling agent-modified nano-carbon black mixed slurry: mixing nano-carbon black with an inactive diluent, pre-dispersing the nano-carbon black with a high-speed disperser, treating the carbon black mixture with an ultrasonic device, adding the silane coupling agent to the carbon black mixture, stirring uniformly, and separating the mixture by centrifugation or filtration after the reaction to obtain a nano-carbon black mixed slurry;

[0041] S3, preparing a modified nano-carbon black / carbon fiber conductive composite material: weighing carbon fiber, toughening agent, lubricant, and the remainder of inactive diluent respectively, adding them to the nano-carbon black mixture prepared in step S2, and mixing them evenly to obtain a nano-carbon black / carbon fiber conductive composite material;

[0042] S4. Weigh the flaky silver powder, spherical silver powder, and surface treatment agent respectively, and stir to obtain pretreated silver powder;

[0043] S5. Add the nano carbon black / carbon fiber conductive composite material, pretreated silver powder, and dispersant into a mixing device, and stir to obtain a first mixture.

[0044] S6. Weigh the graphene oxide modified epoxy resin and the remaining amount of the silane coupling agent respectively, add them to the first mixture, and stir to obtain a second mixture.

[0045] S7. Weigh the curing agent and curing accelerator separately, add them to the second mixture, stir, grind and disperse, and perform vacuum degassing to obtain an epoxy resin encapsulation adhesive material with high bonding stability.

[0046] In some embodiments of the present invention, in step S2, the rotation speed of the high-speed disperser is 1500-2000 r / min, and the pre-dispersion is 10-20 minutes; the vibration frequency of the ultrasonic equipment is 20kHz-40kHz, and the vibration time is 15-30 minutes; the temperature during uniform stirring is controlled at 60-100°C.

[0047] In some embodiments of the present invention, in step S4, the stirring time is 15 to 30 minutes, and the stirring speed is 100 to 300 r / min.

[0048] In some embodiments of the present invention, in step S5, the stirring time is 15 to 30 minutes, and the stirring speed is 100 to 300 r / min.

[0049] In some embodiments of the present invention, in some embodiments of the present invention, in step S6, the stirring time is 10 to 15 minutes, and the stirring speed is 100 to 300 r / min.

[0050] In some embodiments of the present invention, in step S7, the stirring time is 5 to 10 minutes, and the stirring speed is 100 to 300 r / min; the grinding and dispersion is performed using a three-roll grinder until the conductive adhesive particles have a fineness of no more than 5 μm.

[0051] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0052] First, the technical solution of the present invention adopts graphene oxide to modify epoxy resin, which provides a new idea for improving the dispersion stability of graphene oxide filler and the electrical conductivity and thermal conductivity of composite conductive connecting materials. (1) Graphene oxide modified epoxy resin can improve the dispersion stability of graphene oxide in the epoxy resin matrix, enhance the interfacial interaction between graphene oxide and the epoxy resin matrix, and improve the overall mechanical, thermal and anti-corrosion properties of the composite material. Graphene oxide is the product of graphene oxidation. It is a new type of carbon material with excellent performance. It has a large specific surface area and contains rich oxygen-containing functional groups on the surface, such as hydroxyl, epoxy and carboxyl groups. These functional groups give it good hydrophilicity and reactivity, improve the compatibility of graphene oxide with epoxy resin, make graphene oxide easier to combine with polymers, enhance the interaction between graphene oxide and polymers, thereby improving its dispersion stability and avoiding the phenomenon of graphene particle agglomeration. (2) Graphene oxide modified epoxy resin can improve conductivity. Adding a small amount of graphene oxide to epoxy resin can improve the conductivity and electromagnetic properties of the material. Graphene oxide forms a conductive network channel in epoxy resin. When the content of conductive filler is higher than the percolation threshold, this conductive path will be formed, thereby improving the conductivity of the composite material. This study found that when the addition amount of graphene oxide is 0.1-0.5%, the conductivity of the composite material gradually increases. Graphene oxide modified epoxy resin has a significant effect in improving conductivity, which provides a broader prospect for the application of epoxy resin in electronics, aviation and other fields. (3) Graphene oxide modified epoxy resin can improve thermal conductivity. Specifically, there are three mechanisms of action: ① Constructing a thermal conductive network. Graphene oxide has high thermal conductivity. Adding graphene oxide as a thermal conductive filler to epoxy resin can form a thermal conductive network in the polymer, thereby improving the thermal conductivity of the composite material. ② Reducing interfacial thermal resistance. The addition of graphene oxide can reduce the interfacial thermal resistance between the filler and the resin matrix, which is also one of the key factors in improving the thermal conductivity of the composite material. ③ Producing a synergistic effect. When graphene oxide is used together with other fillers (such as carbon nanotubes), a synergistic effect can be achieved, further improving the thermal conductivity of epoxy resin. When the graphene oxide addition level is low, the improvement in thermal conductivity is more significant. This study shows that when the mass fraction of graphene oxide is 0.1%, 0.3%, 0.5%, 0.7%, and 1%, the thermal conductivity of epoxy resin composites increases from 0.19 W / (m·K) of pure epoxy resin to 0.52, 0.99, 1.22, 1.33, and 1.42 W / (m·K), respectively. As the graphene oxide addition level increases, the improvement in thermal conductivity gradually decreases, but the overall upward trend persists.

[0053] Second, the technical solution of the present invention uses silane coupling agent modified nano carbon black as a short-range conductive additive and carbon fiber as a long-range conductive additive, and utilizes the synergistic effect of nano carbon black and carbon fiber. By matching reasonable toughening agents, lubricants, inactive diluents, etc., according to a certain mass ratio, a nano carbon black / carbon fiber conductive composite material with excellent conductivity, high tensile strength and bending strength can be obtained. Nano carbon black has a small particle size and a large specific surface area, and is easy to disperse in the matrix to form a dense short-range conductive network, but when used alone, a high addition amount is required to reach the percolation threshold; carbon fiber has a large aspect ratio and excellent conductivity (resistivity of about 10 -3 ~10 -4 Ω·cm), which can form a long-range conductive path in the matrix, but when used alone, it may cause local conductivity differences due to uneven fiber dispersion. When nano carbon black is compounded with carbon fiber as a conductive filler, the nano carbon black fills the gaps between the carbon fibers, makes up for the areas that are difficult for long fibers to cover, reduces the overall percolation threshold, forms a more continuous three-dimensional conductive network, produces a synergistic conductive effect, and improves the conductive properties of nano carbon black / carbon fiber conductive composite materials. At the same time, carbon fiber can improve the mechanical strength (such as tensile strength and bending) of the composite material. The mechanical strengthening effect of carbon fiber combined with the dispersibility of carbon black helps to improve the tensile strength and bending strength of the material. Ultrasonic treatment of carbon black using high-frequency vibration and then chemical grafting modification of carbon black with a silane coupling agent can not only ensure the uniform dispersion of nano carbon black, but also improve the interfacial bonding between carbon black and the basic resin.

[0054] Third, the silver powder used in the technical solution of the present invention is a compound of flaky silver powder and spherical silver powder, and the surface of the silver powder is chemically coated with a surface treatment agent such as stearic acid to obtain a conductive adhesive material with stable dispersion and synergistically improved conductivity, processability and economy. Flaky silver powder and spherical silver powder each have advantages and disadvantages in terms of conductivity and mechanical properties. The flaky silver powder has a larger specific surface area, and the particles form a conductive path through line contact or surface contact, and the resistivity is lower; the spherical silver powder has a smaller specific surface area, and the particles conduct electricity only through point contact, so the conductivity of the spherical silver powder is slightly weaker. The flaky silver powder has a wide deflection range and strong anti-fracture performance, which can improve the reliability of electronic components; the spherical silver powder has a lower film shrinkage rate after sintering, which is suitable for application scenarios that are sensitive to deformation. When flaky silver powder is compounded with spherical silver powder, the flaky silver powder forms a low-resistance path through surface contact or line contact. Its large specific surface area and arrangement are more conducive to electron transfer. At the same mass, its volume resistivity is lower than that of spherical silver powder. Spherical silver powder can fill the gaps between flaky silver powders, so that adjacent silver sheets that were originally not in contact form parallel conductive paths, further reducing the overall contact resistance. Flake silver powder provides a base conductive network, while spherical silver powder enhances the efficiency of electron transfer in three-dimensional space. The combination of the two forms a denser conductive path. The compound system of spherical silver powder and flaky silver powder can reduce the total amount of silver powder and reduce material costs while ensuring performance by optimizing the conductive network structure. Therefore, the compounding of flaky and spherical silver powders achieves a synergistic improvement in conductivity, processability, and economy through geometric complementarity and conductive path optimization. Stearic acid is used to chemically coat the surface of flaky / spherical composite silver powder to form a spatial isolation layer. The stearic acid molecules are bound to the silver surface through carboxyl groups, and their long-chain alkyl groups provide an anti-aggregation effect, which can effectively reduce the agglomeration of silver powder particles and delay oxidation, thereby improving its dispersibility and other properties. DETAILED DESCRIPTION

[0055] The present invention will be further described below in conjunction with specific embodiments. In the following examples and comparative examples, substances with the same name have the same substance type and source.

[0056] Example A1

[0057] A1 is a technical solution using graphene oxide modified epoxy resin (this patented technology), and the amount of graphene oxide modified epoxy resin used is 13 (weight percentage).

[0058] The preparation process of A1 is as follows:

[0059] (1) Preparation of graphene oxide modified epoxy resin. ① Graphene oxide was prepared by the improved Hummers method. Graphite powder, concentrated sulfuric acid and phosphoric acid were stirred and mixed in an ice-water bath, and then KMnO4 and H2O2 were slowly added. The mixture was then washed with 3% hydrochloric acid solution and deionized water until neutral, and finally freeze-dried to obtain the graphene oxide product. ② Preparation of graphene oxide modified epoxy resin. 20 ml of epoxy resin E51 (density 1.16 g / ml) was preheated in a 60°C water bath for 30 minutes to make it a highly fluid liquid. At the same time, 0.3% of graphene oxide (the weight percentage of graphene oxide in epoxy resin) was added to 50 ml of anhydrous ethanol and ultrasonically dispersed for 30 minutes to allow the graphene oxide to be evenly dispersed in the anhydrous ethanol. The anhydrous ethanol solution of graphene oxide was then poured into the epoxy resin and ultrasonically dispersed for 60 minutes. After sufficient dispersion, it was stirred in a 60°C water bath for 30 minutes. Then, the mixture was placed in a vacuum box at 80°C to remove air bubbles and evaporate the anhydrous ethanol for two hours to obtain graphene oxide modified epoxy resin. The resin was set aside.

[0060] (2) Prepare a homemade silane coupling agent-modified nano-carbon black mixed slurry. ① According to the components and weight percentages of "Example A1" specified in Table 1, weigh the weight of nano-carbon black and inactive diluent, and mix the nano-carbon black and inactive diluent in a weight ratio of 10:1. Use a high-speed disperser (1800r / min) to pre-disperse for 15 minutes to ensure that the inactive diluent and nano-carbon black are in uniform contact. ② Use ultrasonic equipment to treat the carbon black mixture with a vibration frequency of 30kHz and a vibration time of 20 minutes; ③ Add 6.0% silane coupling agent to the carbon black mixture in an amount of nano-carbon black by weight, stir evenly, control the temperature at 80°C, and separate by centrifugation or filtration after the reaction to obtain a nano-carbon black mixed slurry.

[0061] (3) Preparation of a modified nano-carbon black / carbon fiber conductive composite material. According to the weight percentages of the components and the corresponding weight percentages of "Example A1" specified in Table 1, weigh the carbon fibers, toughening agent, lubricant, and the remaining amount of inactive diluent, add them to the homemade nano-carbon black mixed slurry, and mix thoroughly to obtain the homemade nano-carbon black / carbon fiber conductive composite material. Set aside.

[0062] (4) According to the dosage of the formula, weigh the flaky silver powder, spherical silver powder, and surface treatment agent stearic acid respectively, and stir at a low speed of 200 r / min for 20 minutes to obtain pretreated silver powder. Set aside.

[0063] (5) According to the formula, the homemade nano carbon black / carbon fiber conductive composite material, pretreated silver powder, and dispersant were added to the mixing equipment and stirred at a low speed for 20 minutes to obtain a first mixture.

[0064] (6) According to the formula, the homemade graphene oxide modified epoxy resin, the remaining amount of silane coupling agent, and the active diluent were weighed respectively, added to the first mixture, and stirred at a low speed for 10 minutes to obtain a second mixture.

[0065] (7) Weigh the curing agent and curing accelerator according to the formula, add them to the second mixture, and stir at low speed for 8 minutes. Grind and disperse the conductive adhesive using a three-roll mill until the particle size does not exceed 5 μm. Vacuum degassing is performed to obtain an epoxy resin encapsulation adhesive material with high bonding stability.

[0066] Comparative Example B1

[0067] B1 is a technical solution using graphene-modified epoxy resin, and the amount of graphene-modified epoxy resin used is 13 (weight percentage).

[0068] The preparation process of B1 is as follows:

[0069] (1) Preparation of graphene-modified epoxy resin. ① Commercially available graphene was selected for the subsequent epoxy resin modification experiment. The graphene used in this study had a purity greater than 97 wt%, a diameter not exceeding 6 μm, a number of layers less than 10, and a specific surface area of ​​80 to 120 m 2 / g range, it is used as an external admixture of epoxy resin to improve the thermal conductivity of the composite material. ② Preparation of graphene-modified epoxy resin. Preheat 20 ml of epoxy resin E51 (density 1.16 g / ml) in a 60 ° C water bath for 30 minutes to make it a highly fluid liquid. At the same time, add 0.3% of graphene (the weight percentage of graphene oxide in epoxy resin) to 50 ml of anhydrous ethanol and ultrasonically disperse for 30 minutes to allow the graphene to be evenly dispersed in anhydrous ethanol. Then pour the graphene anhydrous ethanol solution into the epoxy resin and ultrasonically disperse for 60 minutes. After sufficient dispersion, stir in a 60 ° C water bath for 30 minutes. Then put it into a vacuum box at 80 ° C, vacuum to degas, evaporate the anhydrous ethanol, and keep it for two hours to obtain graphene-modified epoxy resin. Set aside.

[0070] (2) The rest of the experimental process is the same as steps (2) to (7) in Example 1.

[0071] Comparative Example C1

[0072] C1 is a technical solution using unmodified epoxy resin, and the amount of unmodified epoxy resin used is 13 (weight percentage).

[0073] The preparation process of C1 is as follows:

[0074] (1) Prepare 500 mL of epoxy resin E51 (density 1.16 g / ml). Set aside.

[0075] (2) The rest of the experimental process is the same as steps (2) to (7) in Example 1.

[0076] Example A2

[0077] A2 also utilizes graphene oxide-modified epoxy resin (the technology of this patent), but uses 10% by weight of the graphene oxide-modified epoxy resin. The components are weighed according to the weight percentages of "Example A2" specified in Table 1. Aside from the weight percentages of the components, the preparation method is otherwise identical to Example A1.

[0078] Example A3

[0079] A3 is a technical solution using graphene oxide-modified epoxy resin (the technology of this patent), with the amount of graphene oxide-modified epoxy resin used being 16 (weight percent). The components of "Example A3" and their weight percentages specified in Table 1 were weighed. Aside from the different weight percentages of the components, the preparation method was otherwise identical to Example A1.

[0080] Comparative Example B2

[0081] B2 is a technical solution using a graphene-modified epoxy resin, with the amount of graphene-modified epoxy resin being 10% by weight. The components of "Comparative Example B2" and their weight percentages specified in Table 1 were weighed. The preparation method was identical to Comparative Example B1, except for the different weight percentages of the components.

[0082] Comparative Example B3

[0083] B3 is a technical solution using a graphene-modified epoxy resin, with the amount of graphene-modified epoxy resin used being 16 (weight percent). The components of "Comparative Example B3" were weighed according to their weight percentages specified in Table 1. The preparation method was identical to Comparative Example B1, except for the different weight percentages of the components.

[0084] Comparative Example C2

[0085] C2 utilizes an unmodified epoxy resin, using 10 weight percent of the unmodified epoxy resin. The components of "Comparative Example C2" were weighed according to their weight percentages as specified in Table 1. The preparation method was identical to Comparative Example C1, except for the weight percentages of the components.

[0086] Comparative Example C3

[0087] C3 utilizes an unmodified epoxy resin, using 16 weight percent of the unmodified epoxy resin. The components of "Comparative Example C3" were weighed according to their weight percentages as specified in Table 1. The preparation method was identical to Comparative Example C1, except for the weight percentages of the components.

[0088] Comparative Example D

[0089] D is commercially available epoxy conductive silver glue.

[0090] According to the weight ratios in Table 1, samples of Examples A1-A3, Comparative Examples B1-B3, and Comparative Examples C1-C3 were prepared, and parallel experiments were conducted with Comparative Example D, a commercially available similar product, to test the dispersion state, thermal conductivity, electrical conductivity, and mechanical properties of the conductive adhesive. The thermal conductivity of the conductive adhesive was tested using Anatech Phase 11 according to ASTM E-1461. The volume resistivity of the conductive adhesive was tested using a four-probe multimeter according to GB / T 1410-2006. The tensile strength and flexural strength of the conductive adhesive were tested in accordance with the national standard GB / T 2567-2008. The test results are shown in Table 1.

[0091] Table 1 Effects of unmodified epoxy resin and epoxy resin modified by different methods on the properties of conductive adhesive materials

[0092]

[0093]

[0094] Comparing the data in Table 1 shows that the conductive adhesive materials produced using graphene oxide-modified epoxy resin technology (Examples A1-A3) exhibit uniform dispersion of conductive particles, with no agglomeration or precipitation. However, the conductive adhesive materials produced using graphene-modified epoxy resin technology (Comparative Examples B1-B3) exhibit uneven dispersion of conductive particles, with significant agglomeration or precipitation. The commercially available epoxy resin conductive silver adhesive (Comparative Example D) exhibits excellent dispersion, with no significant agglomeration or precipitation.

[0095] Examples A1-A3 have excellent thermal conductivity, with thermal conductivity coefficients (W / (m·K)) of 19.3, 18.7, and 19.8, respectively, which are higher than those of Comparative Examples B1-B3 (15.5, 15.3, and 15.6), and higher than those of Comparative Examples C1-C3 (13.9, 13.5, and 14.1), and even higher than that of Comparative Example D (only 9.8), a similar product on the market.

[0096] Examples A1-A3 have excellent electrical conductivity, with volume resistivity (Ω·cm) of 0.7×10 -4 , 0.8×10 -4 , 0.6×10-4 , which is significantly smaller than that of comparative examples B1-B3 (1.0×10 -4 , 1.1×10 -4 , 0.9×10 -4 ), and is also smaller than that of Comparative Examples C1-C3 (1.2×10 -4 , 1.4×10 -4 , 1.1×10 -4 ), which is much smaller than the comparative example D (2.3×10 -4 ).

[0097] Comparing the data in Table 1 shows that the conductive adhesive materials produced using graphene oxide-modified epoxy resin technology (Examples A1-A3) exhibit uniform dispersion of conductive particles, with no agglomeration or precipitation. However, the conductive adhesive materials produced using graphene-modified epoxy resin technology (Comparative Examples B1-B3) exhibit uneven dispersion of conductive particles, with significant agglomeration or precipitation. The commercially available epoxy resin conductive silver adhesive (Comparative Example D) exhibits excellent dispersion, with no significant agglomeration or precipitation.

[0098] Examples A1-A3 exhibit excellent mechanical properties, with both flexural and tensile strengths exceeding those of Comparative Examples B1-B3 and Comparative Examples C1-C3, and significantly exceeding that of a similar commercial product, Comparative Example D. The adhesive colloid itself is not easily damaged, resulting in high bonding stability. The conductive adhesives (Examples A1-A3) produced using graphene oxide-modified epoxy resin technology achieved flexural strengths of 133 MPa, 136 MPa, and 128 MPa, respectively, and tensile strengths of 51 MPa, 53 MPa, and 50 MPa, respectively. These strengths are significantly higher than the flexural strength (83 MPa) and tensile strength (35 MPa) of a similar commercial product, Comparative Example D.

[0099] In order to investigate the effects of the modified nano-carbon black with a silane coupling agent and different weight ratios of the nano-carbon black and the carbon fiber on the performance of the conductive adhesive material according to the technical solution of the present invention, the following examples and comparative examples are compared for the conductive adhesive materials prepared by Example A4 (preferred method of this patent), Example A5 (general method of this patent), Example A6 (general method of this patent), Comparative Example B4, Comparative Example B5, Comparative Example B6, Comparative Example C4, Comparative Example D4, and commercially available epoxy resin conductive silver paste (Comparative Example E).

[0100] Example A4

[0101] A4 uses a silane coupling agent to modify nanocarbon black and carbon fiber. The weight ratio of nanocarbon black to carbon fiber is 1:1 (the preferred method of this patent). The nanocarbon black used has been modified with a silane coupling agent, and the amount of silane coupling agent used is 1.2 (weight percent). The preparation process is the same as that of Example A1.

[0102] Comparative Example B4

[0103] B4 uses a technical solution of compounding unmodified nano carbon black with carbon fiber. The weight ratio of unmodified nano carbon black to carbon fiber is 1:1.

[0104] The preparation process of B4 is as follows:

[0105] (1) Preparation of graphene oxide-modified epoxy resin: The same as step (1) in Example A1.

[0106] (2) Preparation of a nanocarbon black / carbon fiber conductive composite material. According to the components and weight percentages of "Comparative Example B4" specified in Table 2, weigh the nanocarbon black, carbon fiber, toughening agent, lubricant, and inactive diluent, mix them uniformly, and obtain a homemade nanocarbon black / carbon fiber conductive composite material. Set aside.

[0107] (3) According to the dosage of the formula, weigh the flaky silver powder, spherical silver powder, and surface treatment agent stearic acid respectively, and stir at a low speed of 200 r / min for 20 minutes to obtain pretreated silver powder. Set aside.

[0108] (4) According to the formula, the homemade nano carbon black / carbon fiber conductive composite material, pretreated silver powder, and dispersant were added to a mixing device and stirred at a low speed for 20 minutes to obtain a first mixture.

[0109] (5) According to the formula, the homemade graphene oxide modified epoxy resin and the active diluent were weighed and added to the first mixture, and stirred at a low speed for 10 minutes to obtain a second mixture.

[0110] (6) Weigh the curing agent and curing accelerator according to the formula, add them to the second mixture, and stir at low speed for 8 minutes. Grind and disperse the conductive adhesive using a three-roll mill until the particle size does not exceed 5 μm. Vacuum degassing is performed to obtain an epoxy resin encapsulation adhesive material with high bonding stability.

[0111] Comparative Example C4

[0112] Comparative Example C4 adopts the technical solution of modifying nano carbon black with a silane coupling agent but not adding carbon fibers, and the amount of the silane coupling agent used is 1.2 (weight percent).

[0113] The preparation process of C4 is as follows:

[0114] (1) Preparation of graphene oxide-modified epoxy resin: The same as step (1) in Example A1.

[0115] (2) Prepare a silane coupling agent-modified nano-carbon black mixed slurry. This is the same as step (2) in Example A1.

[0116] (3) Preparation of modified nanocarbon black conductive material. According to the components and weight percentages of "Comparative Example C4" specified in Table 2, weigh the toughening agent, lubricant, and the remaining amount of inactive diluent, mix them evenly, and obtain the homemade modified nanocarbon black conductive material. Set aside.

[0117] (4) to (7) are the same as steps (4) to (7) in Example A1.

[0118] Comparative Example D4

[0119] Comparative Example D4 uses a technical solution in which only carbon fibers are used without adding nano carbon black. The amount of silane coupling agent used is 9.0 (weight percent). The preparation process is as follows:

[0120] (1) Preparation of graphene oxide-modified epoxy resin: The same as step (1) in Example A1.

[0121] (2) Self-made carbon fiber conductive material. According to the components and weight percentages of "Comparative Example D4" specified in Table 2, weigh the carbon fiber, toughening agent, lubricant, and inactive diluent respectively, mix them evenly, and obtain the self-made carbon fiber conductive material. Set aside.

[0122] (3) to (6) are the same as steps (4) to (7) in Example A1.

[0123] Example A5

[0124] A5 uses a silane coupling agent to modify nanocarbon black and compound it with carbon fibers. The weight ratio of nanocarbon black to carbon fibers is 1:2 (the general method of this patent). The nanocarbon black used is modified with a silane coupling agent, and the amount of silane coupling agent used is 1.2 (weight percent). The preparation process is the same as that of Example A4.

[0125] Example A6

[0126] A6 utilizes a silane coupling agent-modified nanocarbon black and carbon fiber composite. The weight ratio of nanocarbon black to carbon fiber is 2:1 (the general method of this patent). The nanocarbon black used is modified with a silane coupling agent, and the amount of silane coupling agent used is 1.2% by weight. The preparation process is the same as that of Example A4.

[0127] Comparative Example B5

[0128] B5 uses a technical solution that combines unmodified nanocarbon black with carbon fibers. The weight ratio of unmodified nanocarbon black to carbon fibers is 1:2. Its preparation process is the same as that of comparative example B4.

[0129] Comparative Example B6

[0130] B6 uses a technical solution of compounding unmodified nano-carbon black with carbon fibers. The weight ratio of unmodified nano-carbon black to carbon fibers is 2:1 (the preferred method of this patent). Its preparation process is the same as that of comparative example B4.

[0131] Comparative Example E

[0132] E is a commercially available epoxy resin conductive silver paste (the sample is the same as that of comparative example D).

[0133] According to the weight ratio in Table 2, samples of Examples A4-A6, Comparative Examples B4-B6, Comparative Example C4, and Comparative Example D4 were prepared respectively, and parallel experiments were carried out with Comparative Example E of a similar product on the market to detect the dispersion state, thermal conductivity, electrical conductivity and mechanical properties of the conductive adhesive. The thermal conductivity coefficient of the conductive adhesive was tested using Anatech Phase 11 according to the ASTM E-1461 standard. The volume resistivity of the conductive adhesive was tested using a four-probe multimeter according to the GB / T 1410-2006 standard. The tensile strength and flexural strength of the conductive adhesive were tested in accordance with the national standard GB / T 2567-2008. The test results are shown in Table 2. Table 2 Effects of silane coupling agent modified carbon black and its different weight ratios to carbon fiber on the performance of conductive adhesive materials

[0134]

[0135]

[0136] By comparing the data in Table 2, it can be seen that the conductive adhesive materials (Examples A4-A6) prepared by the technology of compounding nano-carbon black modified by silane coupling agent and carbon fiber (the method of this patent) have uniform dispersion of conductive particles in the conductive adhesive without agglomeration or precipitation; the conductive adhesives (Comparative Examples B4-B6) prepared by the technology of compounding unmodified nano-carbon black and carbon fiber have uneven dispersion of conductive particles in the conductive adhesive with obvious agglomeration or precipitation. Comparative Example C4 adopts the technical solution of modifying nano-carbon black with a silane coupling agent but not adding carbon fiber. The conductive adhesive material prepared by this solution also has uniform dispersion of conductive particles without agglomeration or precipitation. Comparative Example D4 adopts the technical solution of not adding nano-carbon black and only using carbon fiber. The conductive adhesive material prepared by this solution has a uniform dispersion and dispersion stability of conductive particles similar to that of commercially available epoxy resin conductive silver glue (Comparative Example E4). The conductive particles are well dispersed without obvious agglomeration or precipitation.

[0137] Examples A4-A6 have excellent comprehensive performance, with excellent thermal conductivity, and their thermal conductivity coefficients (W / (m·K) are 19.3, 18.7, and 19.9 respectively; they have excellent electrical conductivity, and their volume resistivity (Ω·cm) is 0.7×10 -4 , 0.8×10 -4 , 0.9×10 -4; It has excellent mechanical properties, with bending strength (MPa) of 133, 136, and 124 respectively, and tensile strength (MPa) of 51, 53, and 48 respectively.

[0138] Compared with Examples A4-A6, Comparative Examples B4-B6 have significant differences in thermal conductivity, electrical conductivity, and mechanical properties due to the lack of surface modification of nano-carbon black using a silane coupling agent. Compared with Examples A4-A6, the thermal conductivity (W / (m·K)) of Comparative Examples B4-B6 decreased to 16.8, 16.3, and 17.4, respectively; the volume resistivity (Ω·cm) increased to 1.2×10 -4 , 1.1×10 -4 , 1.4×10 -4 ; Their bending strength (MPa) dropped to 103, 115, and 101 respectively, and their tensile strength (MPa) dropped to 41, 44, and 40 respectively.

[0139] Comparative Example C4 uses a technical solution in which nano-carbon black is modified with a silane coupling agent but no carbon fiber is added. Comparative Example D4 uses a technical solution in which only carbon fiber is used without adding nano-carbon black. The thermal conductivity of the conductive adhesive materials prepared using these two solutions is similar to that of Example A4. The thermal conductivity coefficients (W / (m·K)) of Comparative Examples C4 and D4 are 19.4 and 19.2, respectively. Compared with Example A4, the conductivity of Comparative Examples C4 and D4 is greatly reduced. Compared with Example A4, the volume resistivity (Ω·cm) of Comparative Examples C4 and D4 increases to 1.1×10 -4 , 1.0×10 -4 From the perspective of mechanical properties, the mechanical properties of Comparative Examples C4 and D4 are also inferior to those of Example A4, with their flexural strength (MPa) dropping to 120 and 128, respectively, and their tensile strength (MPa) dropping to 45 and 47, respectively.

[0140] Compared with Examples A4-A6, the thermal conductivity, electrical conductivity and mechanical properties of the commercially available epoxy resin conductive silver paste (Comparative Example E) are all inferior to those of Examples A4-A6.

[0141] In summary, the conductive adhesive materials (Examples A4-A6) prepared by using the technology of modifying nano-carbon black with a silane coupling agent and compounding it with carbon fibers (the method of this patent) have uniform dispersion of conductive particles without agglomeration or precipitation; they have outstanding electrical conductivity, thermal conductivity, and mechanical properties, and are technical solutions with excellent comprehensive performance. The conductive adhesive materials (Comparative Examples B4-B6) prepared by not using a silane coupling agent to modify the surface of nano-carbon black have uneven dispersion of conductive particles, with obvious agglomeration or precipitation, and their thermal conductivity, electrical conductivity, and mechanical properties are not as good as those of Examples A4-A6. Comparative Example C4 uses a technical solution of modifying nano-carbon black with a silane coupling agent but not adding carbon fibers, and Comparative Example D4 uses a technical solution of using only carbon fibers without adding nano-carbon black. The conductive adhesive materials prepared by these two solutions have thermal conductivity similar to that of Example A4, but their electrical conductivity is greatly reduced, and their mechanical properties are also not as good as those of Example A4. The thermal conductivity, electrical conductivity and mechanical properties of the commercially available epoxy resin conductive silver paste (Comparative Example E4) are inferior to those of Examples A4-A6.

[0142] To investigate the effects of varying weight ratios of flaky to spherical silver powder and chemical coating treatment on the performance of conductive adhesive materials, the following comparisons are made between the conductive adhesive materials prepared using Example A7 (the preferred method of this patent), Example A8 (the general method of this patent), Example A9 (the general method of this patent), Comparative Examples B7, B8, and B9, as well as a commercially available epoxy conductive silver paste (Comparative Example F). Table 3 shows the formulation information and performance test results for each example and comparative example.

[0143] Example A7

[0144] A7 utilizes a blend of flaky and spherical silver powders in a weight ratio of 50:6, and chemically coats the surface of the micron / nanoscale composite silver powder with stearic acid (a preferred method of this patent). The components of "Example A7" are weighed according to their weight percentages as specified in Table 3. The preparation process is the same as that of Example A1.

[0145] Comparative Example B7

[0146] B7 utilizes a 50:6 weight ratio of flaky silver powder to spherical silver powder. In this comparative solution, the surface treatment agent dosage is zero, meaning the silver powder is not subjected to surface chemical coating. The components of "Example B7" and their weight percentages specified in Table 3 were weighed. Aside from the lack of surface treatment on the silver powder, the remaining preparation process was identical to that of Example A7.

[0147] Example A8

[0148] A8 utilizes a composite of flaky and spherical silver powders in a weight ratio of 48:8, and chemically coats the surface of the micron / nanoscale composite silver powder with stearic acid (a general method of this patent). The components of "Example A8" are weighed according to their weight percentages specified in Table 3. The preparation process is the same as that of Example A7.

[0149] Comparative Example B8

[0150] B8 utilizes a 48:8 weight ratio of flaky silver powder to spherical silver powder. In this comparative solution, the surface treatment agent is added at zero, meaning the silver powder undergoes no surface chemical coating. The components of "Example B8" were weighed according to their weight percentages specified in Table 3. The preparation process is the same as that of Example B7.

[0151] Example A9

[0152] A9 utilizes a composite of flaky and spherical silver powders in a weight ratio of 52:4, and chemically coats the surface of the micron / nanoscale composite silver powder with stearic acid (a general method of this patent). The components of "Example A9" are weighed according to their weight percentages as specified in Table 3. The preparation process is the same as that of Example A7.

[0153] Comparative Example B9

[0154] B9 utilizes a weight ratio of flaky silver powder to spherical silver powder of 52:4. In this comparative solution, the surface treatment agent is added at zero concentration, meaning the silver powder undergoes no surface chemical coating. The components of "Example B9" and their weight percentages specified in Table 3 were weighed. The preparation process is the same as that of Example B7.

[0155] Comparative Example F

[0156] F is a commercially available epoxy resin conductive silver paste (the sample is the same as that of comparative example D).

[0157] According to the weight ratios in Table 3, samples of Examples A7-A9 and Comparative Examples B7-B9 were prepared, and parallel experiments were conducted with Comparative Example F, a commercially available similar product, to test the dispersion state, thermal conductivity, electrical conductivity, and mechanical properties of the conductive adhesive. The thermal conductivity of the conductive adhesive was tested using Anatech Phase 11 according to ASTM E-1461. The volume resistivity of the conductive adhesive was tested using a four-probe multimeter according to GB / T 1410-2006. The tensile strength and flexural strength of the conductive adhesive were tested in accordance with the national standard GB / T 2567-2008. The test results are shown in Table 3.

[0158] Table 3 Effects of different weight ratios of flake / spherical silver powder and their surface treatment on the properties of conductive adhesive materials

[0159]

[0160]

[0161] As shown in Table 3, when flake silver powder and spherical silver powder are compounded at a weight ratio of 50:6 and the surface of the micron / nanoscale composite silver powder is chemically coated with stearic acid (the preferred method of this patent), the resulting conductive adhesive material (Example A7) has the best overall performance. Its conductive particles are evenly dispersed without agglomeration or precipitation; it has excellent thermal conductivity, with a thermal conductivity coefficient (W / (m·K)) of 19.3; and excellent electrical conductivity, with a volume resistivity (Ω·cm) of 0.7×10 -4 ; Excellent mechanical properties, its bending strength and tensile strength reach 133MPa and 51MPa respectively.

[0162] Example A8 uses a compounding of flaky silver powder and spherical silver powder at a weight ratio of 48:8, and chemically coats the surface of the micron- / nano-scale composite silver powder with stearic acid (the general method of this patent). Example A9 uses a compounding of flaky silver powder and spherical silver powder at a weight ratio of 52:4, and chemically coats the surface of the micron- / nano-scale composite silver powder with stearic acid (the general method of this patent). Both are good technical solutions. The conductive particles in Examples A8 and A9 are evenly dispersed, without agglomeration or precipitation. Both have excellent conductivity, with a volume resistivity (Ω·cm) of 1.0×10 -4 , 0.9×10 -4 Compared with the technical solution of Example A7, the thermal conductivity of Examples A8 and A9 is slightly reduced, and their thermal conductivity coefficients (W / (m·K) are 18.1 and 18.9, respectively. In terms of the test results of bending strength and tensile strength, Examples A8 and A9 are similar to Example A7. The bending strength of Examples A8 and A9 are 125 MPa and 135 MPa, respectively; the tensile strength is 48 MPa and 53 MPa, respectively.

[0163] Comparative Examples B7, B8, and B9 all use a technical solution of compounding flaky silver powder and spherical silver powder in a certain weight ratio. The weight ratios of the three are 50:6, 48:8, and 52:4, and the compounded silver powders are not chemically surface-coated with stearic acid. The experimental results in Table 3 show that the conductive particles of the three are unevenly dispersed, with obvious agglomeration or precipitation. The agglomeration or precipitation of conductive particles (especially composite silver powder) seriously affects the uniform distribution of conductive particles in the conductive adhesive coating, resulting in a sharp drop in the thermal conductivity and electrical conductivity of the conductive adhesive. The thermal conductivity coefficient (W / (m·K)) of Comparative Examples B7, B8, and B9 decreased to 17.2, 16.3, and 16.6, respectively, and the volume resistivity (Ω·cm) increased to 1.3×10 -4 , 1.5×10 -4 , 1.4×10 -4 Compared with the technical solutions of Examples A7, A8 and A9, the flexural strength and tensile strength of Comparative Examples B7, B8 and B9 also decreased to a large extent. The flexural strength (MPa) of Comparative Examples B7, B8 and B9 decreased to 107, 103 and 109 respectively, and the tensile strength (MPa) decreased to 43, 41 and 46 respectively.

[0164] Compared with the technical solutions of Examples A7-A9, the thermal conductivity, electrical conductivity and mechanical properties of the commercially available epoxy resin conductive silver paste (Comparative Example F) are all inferior to those of the Examples.

[0165] In summary, by compounding flaky silver powder and spherical silver powder in a certain weight ratio and chemically coating the silver powder surface with stearic acid, a dispersion-stable epoxy resin conductive adhesive material with synergistically improved conductivity, processability and economy can be produced. When flaky silver powder and spherical silver powder are compounded, the flaky silver powder provides a base conductive network, forming a low-resistance path through surface contact or line contact; while the spherical silver powder fills the gaps between the flaky silver powders, so that adjacent silver flakes that were originally not in contact form parallel conductive paths, enhancing the electron transmission efficiency in three-dimensional space. The combination of the two forms a denser conductive path, further reducing the overall contact resistance. The surface of the flaky / spherical composite silver powder is chemically coated with stearic acid to form a spatial isolation layer. The stearic acid molecules bind to the silver surface through carboxyl groups, and its long-chain alkyl groups provide an anti-aggregation effect, which can effectively reduce the agglomeration between silver powder particles and delay oxidation, thereby improving its dispersion and other properties.

[0166] In addition, the mechanical strength of the adhesive materials obtained in Examples A1 / A4 / A7, A2, A3, A5, A6, A8, and A9 was tested after being exposed to 85°C / 85% RH for 500 hours, and the retention rates of tensile strength and flexural strength were both higher than 90%.

[0167] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A high bonding stability epoxy resin encapsulation adhesive material, characterized in that: Calculated by weight percentage, the invention comprises the following raw material components: 8-18% of graphene oxide modified epoxy resin, 0.8-4.0% of curing agent, 0-1% of curing accelerator, 0.4-2.0% of silane coupling agent, 2-7% of nano carbon black, 2-7% of carbon fiber, 40-60% of flaky silver powder, 4-8% of spherical silver powder, 4.4-13.6% of surface treatment agent, 4-6% of active diluent, 0.5-1.5% of toughening agent, 0.5-1.5% of dispersant, 0.1-0.5% of lubricant, and balance of inactive diluent.

2. The high bonding stability epoxy resin encapsulation adhesive material according to claim 1, characterized in that: The graphene oxide modified epoxy resin is prepared by the following steps: Step 1: Graphite powder, concentrated sulfuric acid and phosphoric acid are stirred and mixed, then KMnO4 and H2O2 are slowly added, washed until neutral, and finally dried to obtain graphene oxide; Step 2: Preheat the epoxy resin in a water bath to make it a flowable liquid. At the same time, add graphene oxide to anhydrous ethanol and evenly disperse the graphene oxide in the anhydrous ethanol. Then pour the anhydrous ethanol solution of graphene oxide into the epoxy resin, fully disperse it, stir it in a water bath, and then vacuum it to degas the bubbles and evaporate the anhydrous ethanol.

3. The high bonding stability epoxy resin encapsulation adhesive material according to claim 2, characterized in that: In step 1, the graphite powder, concentrated sulfuric acid, and phosphoric acid are stirred and mixed in an ice-water bath, washed to neutrality with a 3% hydrochloric acid solution and deionized water, and dried by freeze-drying; the graphene oxide has a purity greater than 97 wt%, a diameter between 3 and 10 μm, a number of layers less than 5, and a thickness of 0.55 to 2.0 nm; In step 2, the epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and alicyclic epoxy resin; the bisphenol A epoxy resin is at least one of E-51, E-55, E-35, E-42, and E-44; the bisphenol F epoxy resin is at least one of NPEF-170 and DER354; the alicyclic epoxy resin is at least one of S-06E, TT21, and EP-4221-A; the weight percentage of the graphene oxide in the epoxy resin is 0.1-1.0%; the temperature of the water bath is 50-70° C., and the graphene oxide is uniformly dispersed in anhydrous ethanol by ultrasonic dispersion, and the graphene oxide anhydrous ethanol solution and the epoxy resin are fully dispersed; the stirring time in the water bath is 20-40 minutes, and the vacuum degassing is carried out in a vacuum box at 70-90° C. and maintained for 1-2 hours.

4. The high bonding stability epoxy resin encapsulation adhesive material according to any one of claims 1 to 3, characterized in that: The nano carbon black is modified by the silane coupling agent.

5. The high bonding stability epoxy resin encapsulation adhesive material according to claim 4, characterized in that: The nano-carbon black and the inactive diluent are dispersed by high-frequency vibration ultrasound, and then modified by the silane coupling agent; wherein the weight ratio of the nano-carbon black to the inactive diluent used for dispersing the nano-carbon black is 10:1 to 5:1; the silane coupling agent is 2.0 to 6.0% by weight of the nano-carbon black; The particle size of the nano carbon black is 20 to 80 nm.

6. The high bonding stability epoxy resin encapsulation adhesive material according to any one of claims 1 to 3, characterized in that: The carbon fiber has an aspect ratio of 100 to 500 and a diameter of 50 to 200 nm; The weight ratio of the carbon fiber to the nano carbon black is 4:1 to 1:4, preferably 2:1 to 1:

2.

7. The high bonding stability epoxy resin encapsulation adhesive material according to any one of claims 1 to 3, characterized in that: The mass ratio of the spherical silver powder to the flaky silver powder is 1: (5.0~15.0) compound; The average particle size of the flaky silver powder is 2 to 6 μm, and the tap density is 3.8 to 5.6 g / cm 3 ; The average particle size of the spherical silver powder is 0.2 to 0.5 μm, and the tap density is 3.0 to 4.8 g / cm 3 ; The spherical silver powder and the flaky silver powder are pre-treated by surface coating with the surface treatment agent; The surface treatment agent is stearic acid; The weight ratio of the total mass of the spherical silver powder and the flaky silver powder to the surface treatment agent is 1:(0.10-0.15).

8. The high bonding stability epoxy resin encapsulation adhesive material according to any one of claims 1 to 3, characterized in that: The curing agent is at least one of an aromatic amine curing agent, an aliphatic amine curing agent, a polyamide curing agent, and an acid anhydride curing agent; The curing accelerator is at least one of 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole; The silane coupling agent is at least one of vinyl triethyl silane, γ-aminopropyl trimethyl silane, γ-aminopropyl triethyl silane, 3-methacryloxypropyl trimethoxy silane and hexamethylenediaminomethyl trimethoxy silane; The active diluent is at least one of tert-butylphenyl glycidyl ether, phenyl glycidyl ether, benzyl glycidyl ether, trimethylolethane triglycidyl ether, ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, and o-cresyl glycidyl ether; The inactive diluent is at least one of propylene glycol methyl ether acetate, ethylene glycol ethyl ether, ethyl propionate, isobutyl formate, methyl propionate, butyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, n-butanol, and acetone; The toughening agent is at least one of carboxyl-terminated nitrile rubber, core-shell toughening agent, and polysulfide rubber; The dispersant is at least one of polyvinyl alcohol, sodium pyrophosphate, and sodium hexametaphosphate; The lubricant is at least one of EBS, stearic acid, lauric acid, stearamide, and oleamide.

9. The method for preparing a high-bonding-stability epoxy resin encapsulation adhesive material according to any one of claims 1 to 8, characterized in that: The steps include: S1. Preparation of graphene oxide modified epoxy resin: Graphite powder, concentrated sulfuric acid and phosphoric acid are stirred and mixed, and then KMnO4 and H2O2 are slowly added, followed by washing until neutrality, and finally drying to obtain graphene oxide; the epoxy resin is preheated in a water bath to make it a flowable liquid, and the graphene oxide is added to anhydrous ethanol to uniformly disperse the graphene oxide in the anhydrous ethanol; the anhydrous ethanol solution of graphene oxide is then poured into the epoxy resin, and after being fully dispersed, the mixture is stirred in a water bath, and then vacuumed to degas and evaporate the anhydrous ethanol; S2. Preparing a silane coupling agent-modified nano-carbon black mixed slurry: mixing the nano-carbon black with a portion of an inactive diluent, pre-dispersing the mixture using a high-speed disperser, treating the carbon black mixture using an ultrasonic device, adding a portion of the silane coupling agent to the carbon black mixture, stirring uniformly, and separating the mixture by centrifugation or filtration after the reaction to obtain a nano-carbon black mixed slurry; S3, preparing a modified nano-carbon black / carbon fiber conductive composite material: weighing carbon fiber, toughening agent, lubricant, and the remainder of inactive diluent respectively, adding them to the nano-carbon black mixture prepared in step S2, and mixing them evenly to obtain a nano-carbon black / carbon fiber conductive composite material; S4. Weigh the flaky silver powder, spherical silver powder, and surface treatment agent respectively, and stir to obtain pretreated silver powder; S5. Add the nano carbon black / carbon fiber conductive composite material, pretreated silver powder, and dispersant into a mixing device, and stir to obtain a first mixture. S6. Weigh the graphene oxide modified epoxy resin, the remaining amount of the silane coupling agent, and the reactive diluent respectively, add them to the first mixture, and stir to obtain a second mixture. S7. Weigh the curing agent and curing accelerator respectively, add them to the second mixture, stir, grind and disperse, and perform vacuum degassing to obtain an epoxy resin encapsulation adhesive material with high bonding stability.

10. The preparation method according to claim 10, characterized in that: In step S2, the speed of the high-speed disperser is 1500-2000 r / min, and the pre-dispersion is 10-20 minutes; the vibration frequency of the ultrasonic device is 20kHz-40kHz, and the vibration time is 15-30 minutes; the temperature during the stirring is controlled at 60-100°C; In step S4, the stirring time is 15 to 30 minutes, and the stirring speed is 100 to 300 r / min; In step S5, the stirring time is 15 to 30 minutes, and the stirring speed is 100 to 300 r / min; In step S6, the stirring time is 10 to 15 minutes, and the stirring speed is 100 to 300 r / min; In step S7, the stirring time is 5 to 10 minutes, and the stirring speed is 100 to 300 r / min; The grinding and dispersion is carried out using a three-roller grinder until the conductive adhesive particles have a fineness not exceeding 5 μm.

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