High-thermal-conductivity epoxy resin conductive adhesive containing composite conductive filler and preparation method of high-thermal-conductivity epoxy resin conductive adhesive

Abstract

The invention relates to a high-thermal-conductivity epoxy resin conductive adhesive containing a composite conductive filler and a preparation method of the high-thermal-conductivity epoxy resin conductive adhesive. The high-thermal-conductivity epoxy resin conductive adhesive containing the composite conductive filler comprises 6-16% of graphene oxide modified epoxy resin, 0.6-3% of a curing agent, 0-1% of a curing accelerator, 2-7% of epoxidized soybean oil modified single-layer / multi-layer carbon nanotubes, 3-7% of carbon fibers, 3-7% of nano silver powder, 40-70% of micron silver powder, 5.0-15.0% of a surface treating agent, 0.3-2.7% of a coupling agent, 0.5-1.5% of a dispersing agent, 0.1-0.3% of an antioxidant and 0.1-0.3% of a lubricant. 0.5% and the balance of a solvent. The graphene oxide modified epoxy resin and the epoxidized soybean oil modified single-layer / multi-layer carbon nanotubes are utilized to improve the dispersion stability of the filler, the modified single-layer / multi-layer carbon nanotubes are adopted as a short-range conductive additive, the carbon fibers are adopted as a long-range conductive additive, and the graphene oxide modified epoxy resin and the epoxidized soybean oil modified single-layer / multi-layer carbon nanotubes and the carbon fibers cooperate to improve the conductivity. The conductive adhesive disclosed by the invention is high in heat conductivity, low in volume resistivity and high in tensile strength and bending strength, and has a wide application prospect 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 a high-thermal-conductivity epoxy resin conductive adhesive containing composite conductive fillers and a preparation method thereof. Background Art

[0002] With the development of the electronics industry, electronic components are shrinking in size, while the integration of electronic products continues to increase. This has led to increasingly stringent requirements for internal stress, adhesion, thermal conductivity, and electrical properties of electronic device packaging materials. Traditional Pb / Sn solder is widely used due to its excellent performance and low cost. However, Pb / Sn solder can cause irreversible damage to both the environment and the human body. While lead-free solder poses no environmental pollution concerns, its high melting point prevents it from being used for substrates or wire connections that are sensitive to high temperatures, limiting its application in electronic packaging, particularly in smart packaging. Currently, the most promising material to replace solder is conductive adhesive. As a solder alternative, conductive adhesive is an adhesive that combines both electrical conductivity and bonding capabilities. It offers advantages such as being lead-free, having a small bonding gap, a low curing temperature, high resolution, and wide adaptability, and holds great promise for future applications in the electronic packaging industry.

[0003] With the rapid development of emerging technologies such as 5G, Internet of Things, and artificial intelligence, the demand for high-performance and highly integrated chips is increasing. The market for chip packaging and connection materials in China, represented by conductive adhesives, is growing at an average annual rate of 11%, and will exceed 100 billion yuan in 2024. The survey found that due to the widespread shortage of key raw materials, low-level formulation advancement, and backward packaging technology in the industry, domestic materials generally have three major customer pain points, namely poor thermal conductivity, poor electrical conductivity, and poor bonding stability. The thermal conductivity of conductive adhesives currently on the market is usually below 5.0W / m·K (tested according to GB / T1410-2006 standard), and the volume resistivity is above 5.0×10 -4 Ω·cm (tested in accordance with national standard GB / T 1692-2008), the flexural strength does not exceed 80MPa (tested in accordance with GB / T 2567-2008), and the tensile strength does not exceed 35MPa (tested in accordance with GB / T 2567-2008).

[0004] The invention patent with authorization number CN102653668B discloses a silver conductive adhesive for LED packaging and its preparation method. The silver conductive adhesive uses bisphenol F epoxy resin, curing agent, accelerator and coupling agent as the resin matrix. The prepared conductive adhesive for LED packaging has excellent electrical conductivity and thermal conductivity, high efficiency and good reliability. However, bisphenol F epoxy resin is easy to absorb water. The presence of water molecules will cause the performance of bisphenol F epoxy resin to deteriorate in a humid and hot environment, resulting in a high volume resistivity of the conductive adhesive for LED packaging in a humid and hot environment.

[0005] A conductive adhesive for LED packaging and its preparation method are currently available (Publication No.: CN118325555A). The raw materials for preparing this conductive adhesive include micron-sized silver, nano-sized silver powder, graphene, nano-alumina, carboxylated polyacrylamide, bisphenol F epoxy resin, and a curing agent. This conductive adhesive can significantly improve the electron transmission performance of the conductive adhesive for LED packaging in hot and humid environments, thereby reducing the volume resistivity of the conductive adhesive in hot and humid environments. However, the patent does not address the bonding stability of the conductive adhesive.

[0006] 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 good long-term thermal stability and reliability. However, the material cost of this conductive adhesive is clearly uncompetitive in the market.

[0007] Currently, carbon nanotubes (CNTs) are widely used due to their excellent electrical conductivity. However, due to their large surface area, CNTs tend to aggregate and disperse easily. Therefore, when using CNTs to prepare composite materials, technicians typically use strong oxidants such as strong acids to cut the CNTs into short tubes, resulting in open-ended CNTs. The tips of these open CNTs contain a certain number of active groups, such as hydroxyl and carboxyl groups. However, this surface modification has limited effect on the CNTs' interfacial adhesion and dispersibility. Strong acid washing can dissolve and disperse the CNTs on the surface of the aggregates, but it cannot penetrate the aggregates themselves. Furthermore, the acid washing process is lengthy, energy-intensive, and produces large amounts of acidic wastewater, which has negative environmental impacts. Summary of the Invention

[0008] In view of the deficiencies in the prior art, the present invention aims to provide a highly thermally conductive epoxy resin conductive adhesive containing a composite conductive filler, which has good electrical conductivity, thermal conductivity and mechanical properties.

[0009] Another object of the present invention is to provide a method for preparing the high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers.

[0010] To achieve the purpose of the present invention, the present invention provides a high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers, which includes the following raw material components by weight percentage: 6-16% of graphene oxide modified epoxy resin, 0.6-3% of curing agent, 0-1% of curing accelerator, 2-7% of epoxy soybean oil modified single-layer / multi-layer carbon nanotubes, 3-7% of carbon fiber, 3-7% of nano-scale silver powder, 40-70% of micron-scale silver powder, 5.0-15.0% of surface treatment agent, 0.3-2.7% of coupling agent, 0.5-1.5% of dispersant, 0.1-0.3% of antioxidant, 0.1-0.5% of lubricant and the remainder of solvent.

[0011] Among them, graphene oxide-modified epoxy resin is a modified material obtained by doping graphene oxide into epoxy resin. Graphene oxide is the product of graphene oxidation and is a new type of carbon material with excellent performance. It has a large specific surface area and contains a rich surface of oxygen-containing functional groups such as hydroxyl and carboxyl groups. These functional groups make graphene oxide easier to combine with polymers and can effectively improve the interaction between graphene oxide and polymers. Graphene oxide has a physical structure and properties similar to those of graphene. Using it as an external admixture for epoxy resin modification can not only improve the dispersion stability of graphene oxide fillers and avoid the phenomenon of graphene particle agglomeration, but also improve the electrical and thermal conductivity of composite conductive connection materials.

[0012] Epoxidized soybean oil modified single-layer / multi-layer carbon nanotubes are modified materials obtained by treating single-layer carbon nanotubes and / or multi-layer carbon nanotubes with epoxidized soybean oil. Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) each have their own advantages and disadvantages and are suitable for different application scenarios. Single-walled carbon nanotubes are formed by curling up a single layer of graphene sheets and have higher electrical conductivity and mechanical strength. Multi-walled carbon nanotubes are formed by curling up multiple layers of graphene sheets to form a concentric arrangement structure. This multi-layer structure makes it perform better in terms of thermal conductivity and chemical stability. The technical solution of the present invention can adopt single-walled carbon nanotubes and / or multi-walled carbon nanotubes to obtain composite carbon nanotubes with good electrical conductivity, high thermal conductivity and excellent mechanical strength. It is preferred to use single-walled carbon nanotubes and multi-walled carbon nanotubes in an appropriate mass ratio to compound, and a conductive adhesive product with excellent electrical conductivity, thermal conductivity and mechanical strength can be obtained. At present, carbon nanotubes have been widely used because of their excellent electrical conductivity. However, carbon nanotubes have a large specific surface area, are easy to agglomerate, and are difficult to disperse. Therefore, when technicians use carbon nanotubes to prepare composite materials, they generally use strong oxidants such as strong acids to cut carbon nanotubes into short tubes. However, this surface modification has limited improvement on the interfacial adhesion and dispersibility of carbon nanotubes. Moreover, although strong acid washing can dissolve and disperse the carbon nanotubes on the surface of the agglomerates, it cannot enter the agglomerates themselves. What is more serious is that the pickling process is long, energy-consuming, and will bring a large amount of acidic wastewater, which has a negative environmental impact. The technical solution of the present invention uses epoxidized soybean oil to surface treat carbon nanotubes, allowing the carbon nanotubes to form a granular structure and improve dispersibility. Epoxidized soybean oil is made from ordinary soybean oil and has good biological activity and biodegradability. The whole process does not require the use of strong acid to treat the carbon nanotubes to obtain good dispersibility.

[0013] The silver powder in the conductive adhesive is a compound of nano-silver powder and micron-silver powder. The nano-silver powder fills the gaps between the micron-silver powder particles and can form a tight stacking structure with the micron-silver powder, increasing the contact area between the silver powder particles, thereby improving the thermal conductivity and electrical conductivity of the epoxy resin conductive adhesive containing composite conductive fillers. The tight stacking structure is also beneficial to improving the molecular cohesion of the conductive adhesive, thereby improving the bonding performance.

[0014] In some embodiments of the present invention, the conductive adhesive includes the following raw material components by weight percentage: 8-14% of graphene oxide modified epoxy resin, 1.3-2.3% of curing agent, 0-1% of curing accelerator, 3-7% of epoxy soybean oil modified single-layer / multi-layer carbon nanotubes, 3-7% of carbon fiber, 4-6% of nano-scale silver powder, 54-56% of micron-scale silver powder, 5.0-15.0% of surface treatment agent, 0.3-2.7% of coupling agent, 0.5-1.5% of dispersant, 0.1-0.3% of antioxidant, 0.1-0.5% of lubricant and 0.2-7.2% of solvent.

[0015] In some embodiments of the present invention, the graphene oxide-modified epoxy resin is prepared by the following steps: Step 1, preparing graphene oxide by a modified Hummers method: stirring and mixing graphite powder, concentrated sulfuric acid and phosphoric acid in an ice-water bath, then adding KMnO4 and H2O2, washing with hydrochloric acid solution and deionized water until neutral, and finally freeze-drying to obtain graphene oxide; Step 2, preparing graphene oxide-modified epoxy resin: preheating the epoxy resin to make it liquid, adding graphene oxide to anhydrous ethanol, and ultrasonically dispersing it; then pouring the anhydrous ethanol solution of graphene oxide into the epoxy resin, ultrasonically dispersing it, and after sufficient dispersion, stirring while the epoxy resin remains liquid, then placing it in a vacuum box, evacuating the air bubbles, and volatilizing the anhydrous ethanol.

[0016] In some embodiments of the present invention, in step 1, KMnO 4 and H 2 O 2 are added slowly, and the concentration of the hydrochloric acid solution is 1-5%.

[0017] In some embodiments of the present invention, in step 1, the purity of the graphene oxide obtained is greater than 97 wt %, the diameter is between 3 and 10 μm, the number of layers is less than 5, and the thickness is 0.55 to 2.0 nm.

[0018] In some embodiments of the present invention, the epoxy resin is bisphenol A epoxy resin, bisphenol F epoxy resin, or a cycloaliphatic 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; and the alicyclic epoxy resin is one of S-06E, TT21, and EP-4221-A.

[0019] In some embodiments of the present invention, the preheating temperature of the epoxy resin is 60-80° C., and the preheating time is 20-40 minutes; the weight percentage of graphene oxide in the epoxy resin is 0.1-1.0%; the volume ratio of anhydrous ethanol to epoxy resin is (2-3):1; the ultrasonic dispersion time of graphene oxide in anhydrous ethanol is 20-40 minutes; the ultrasonic dispersion time of the anhydrous ethanol solution of graphene oxide in the epoxy resin is 50-80 minutes, and the stirring is carried out in a water bath at 60-80° C. for 20-40 minutes; the temperature of the vacuum box is 78-90° C., and the vacuum is maintained for 1-3 hours.

[0020] In some embodiments of the present invention, the epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes are prepared by surface-treating and modifying single-walled / multi-walled carbon nanotubes with epoxy soybean oil.

[0021] In some embodiments of the present invention, the epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes are prepared by the following steps: first dissolving the epoxy soybean oil in acetone, then adding the single-walled / multi-walled carbon nanotubes, and stirring evenly to obtain granular epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes.

[0022] In some embodiments of the present invention, the single-walled / multi-walled carbon nanotubes are compounded by single-walled carbon nanotubes and multi-walled carbon nanotubes in a weight ratio of 1:(2.0-8.0).

[0023] In some embodiments of the present invention, the single-walled carbon nanotube has a diameter of 0.5 to 3 nm, a length of 1 to 50 μm, and an aspect ratio of 200 to 400,000.

[0024] In some embodiments of the present invention, the multi-walled carbon nanotubes have a diameter of 10 to 60 nm, a length of 1 to 30 μm, and an aspect ratio of 1,000 to 1,000,000.

[0025] In some embodiments of the present invention, the weight ratio of the single-walled / multi-walled carbon nanotubes, the epoxy soybean oil, and the acetone is 1:(1.0-1.5):(3-5).

[0026] In some embodiments of the present invention, the carbon fiber has an aspect ratio of 100-500, a diameter of 50-200 nm, and an aspect ratio of 30-300.

[0027] In some embodiments of the present invention, the weight ratio of the carbon fibers to the epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes is 3:7 to 7:3, preferably 1:1.

[0028] In some embodiments of the present invention, the nano-scale silver powder and the micro-scale silver powder are coated with the surface treatment agent. Chemically coating the silver powder surface with the surface treatment agent to form a spatial isolation layer can effectively reduce silver powder agglomeration and delay oxidation, thereby improving its dispersibility and other properties.

[0029] In some embodiments of the present invention, the nano-scale silver powder and the micron-scale silver powder are compounded in a mass ratio of 1:(8.0-14.0).

[0030] In some embodiments of the present invention, the nano-scale silver powder and the micron-scale silver powder constitute silver powder, and the weight ratio of the silver powder to the surface treatment agent is 1:(0.1-0.5).

[0031] In some embodiments of the present invention, the particle size of the nano-scale silver powder may be at least one of 20 to 100 nm; and the particle size of the micron-scale silver powder may be 1 to 5 μm.

[0032] 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 isolate the particles, reduce particle aggregation, and delay oxidation.

[0033] 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.

[0034] 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.

[0035] In some embodiments of the present invention, the solvent is at least one of glycidyl ether, ethyl propionate, isobutyl formate, methyl propionate, butyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, and n-butanol.

[0036] In some embodiments of the present invention, the coupling agent is a silane coupling agent, and the silane coupling agent is at least one of vinyltriethylsilane, γ-aminopropyltrimethylsilane, γ-aminopropyltriethylsilane, 3-methacryloxypropyltrimethoxysilane and hexamethylenediaminomethyltrimethoxysilane.

[0037] In some embodiments of the present invention, the dispersant is at least one of polyvinyl alcohol, sodium pyrophosphate, and sodium hexametaphosphate.

[0038] In some embodiments of the present invention, the antioxidant is a mixture of phenolic antioxidant 1010 and antioxidant 168 in a weight ratio of 1:(0.6-1.2). The combination of these two antioxidants has a significant synergistic effect, high anti-oxidative aging and thermal stability.

[0039] In some embodiments of the present invention, the lubricant is at least one of EBS, stearic acid, lauric acid, stearamide, and oleamide.

[0040] To achieve another object of the present invention, the present invention provides a method for preparing the high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers as described in any of the above schemes, which comprises the following steps:

[0041] S1. Preparation of graphene oxide modified epoxy resin: Graphite powder, concentrated sulfuric acid and phosphoric acid are stirred and mixed in an ice-water bath, and then KMnO4 and H2O2 are added, followed by washing with hydrochloric acid solution and deionized water until neutral, and finally freeze-drying to obtain graphene oxide; the epoxy resin is preheated to make it liquid, and the graphene oxide is added to anhydrous ethanol and ultrasonically dispersed; then the anhydrous ethanol solution of graphene oxide is poured into the epoxy resin, ultrasonically dispersed, and after sufficient dispersion, stirred while the epoxy resin remains liquid, and then placed in a vacuum box, evacuated to degas, and the anhydrous ethanol is volatilized;

[0042] S2. Preparing epoxidized soybean oil-modified single-wall / multi-wall carbon nanotubes: Weighing single-wall / multi-wall carbon nanotubes, epoxidized soybean oil, and acetone separately; dissolving the epoxidized soybean oil in acetone, then adding the single-wall / multi-wall carbon nanotubes, and stirring evenly to obtain granular epoxidized soybean oil-modified single-wall / multi-wall carbon nanotubes;

[0043] S3. Weighing epoxy soybean oil-modified single-layer / multi-layer carbon nanotubes, carbon fibers, an antioxidant, a lubricant, and a portion of the solvent, respectively, and mixing them uniformly to obtain a carbon nanotube / carbon fiber conductive composite material;

[0044] S4. Weigh nano-scale silver powder, micron-scale silver powder, and a surface treatment agent respectively, and stir to obtain pretreated silver powder;

[0045] S5. Weigh the carbon nanotube / carbon fiber conductive composite material, pretreated silver powder, dispersant, and another portion of solvent, add them to a mixing device, and stir to obtain a first mixture;

[0046] S6. Weighing graphene oxide-modified epoxy resin and coupling agent respectively, adding them to the first mixture, and stirring to obtain a second mixture;

[0047] S7. Weigh the curing agent and curing accelerator separately, add them to the second mixture, stir, grind and disperse, and perform vacuum degassing to prepare a high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 in a three-roll grinder until the conductive adhesive particles have a fineness of no more than 5 μm.

[0052] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0053] 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.

[0054] Second, the technical solution of the present invention uses epoxidized soybean oil to surface-modify compounded single-walled / multi-walled carbon nanotubes, resulting in composite carbon nanotubes with good electrical conductivity, high thermal conductivity, excellent mechanical strength, and good dispersibility. Single-walled carbon nanotubes are formed by curling a single layer of graphene sheets and have higher electrical conductivity and mechanical strength. Multi-walled carbon nanotubes are formed by curling multiple layers of graphene sheets into a concentrically arranged structure. This multilayer structure enables them to perform better in terms of thermal conductivity and chemical stability. This study compounded single-walled carbon nanotubes and multi-walled carbon nanotubes in a weight ratio of 1:2.0 to 8.0 to produce composite carbon nanotubes with good electrical conductivity, high thermal conductivity, and excellent mechanical strength. Considering that carbon nanotubes have a large specific surface area, are easy to agglomerate and difficult to disperse, technicians generally use strong oxidants such as strong acids to cut carbon nanotubes into short tubes when using carbon nanotubes to prepare composite materials. However, this surface modification has limited improvement on the interfacial adhesion and dispersibility of carbon nanotubes. Moreover, although strong acid washing can dissolve and disperse the carbon nanotubes on the surface of the agglomerates, it cannot enter the agglomerates themselves. What is more serious is that the pickling process is long, energy-intensive, and produces a large amount of acidic wastewater, which has a negative environmental impact. The technical solution of the present invention uses epoxidized soybean oil to surface treat carbon nanotubes, allowing the carbon nanotubes to form a granular structure and improve dispersibility. Epoxidized soybean oil is made from ordinary soybean oil and has good biological activity and biodegradability. The entire process does not require the use of strong acids to treat the carbon nanotubes to obtain good dispersibility.

[0055] Third, the technical solution of the present invention uses homemade epoxy soybean oil modified single-layer / multi-layer carbon nanotubes as a short-range conductive additive, and carbon fibers as a long-range conductive additive. By utilizing the synergistic effect of carbon fibers and carbon nanotubes, and by combining reasonable antioxidants, lubricants, solvents, etc., according to a certain mass ratio, a carbon nanotube / carbon fiber conductive composite material with excellent conductivity, high tensile strength and bending strength can be obtained. Modified single-layer / multi-layer carbon nanotubes can be used as a short-range conductive agent, which has significant advantages in short-range conductive applications and can effectively improve the conductive properties of the material. It is suitable for use in situations where efficient conductive network construction and impedance reduction are required. Carbon nanotubes have an ultra-high aspect ratio and excellent flexibility, which makes it easy to build an efficient conductive network in polymer materials; even if only a small amount of carbon nanotubes is added, the conductivity of the polymer material can be significantly improved. Carbon fibers can be used as a long-range conductive agent to form a synergistic effect with modified single-layer / multi-layer carbon nanotubes, significantly improving the conductive properties of the material. In addition, carbon fiber also has the effect of strengthening and toughening. Compared with carbon nanotube materials without added carbon fiber, the tensile strength and bending strength of carbon nanotube / carbon fiber conductive composite materials are greatly improved, turning the conductive material from the original brittle material into a tough material.

[0056] Fourth, the silver powder used in the technical solution of the present invention is a compound of nano silver powder and micron silver powder, and the surface of the silver powder is chemically coated with stearic acid to obtain an epoxy resin conductive adhesive with stable dispersion, good thermal conductivity, good electrical conductivity and high bonding strength. When nano silver powder and micron silver powder are compounded and used, the nano silver powder fills the gaps between the particles of the micron silver powder, and can form a tight stacking structure with the micron silver powder, increasing the contact area between the silver powder particles, thereby improving the thermal conductivity and electrical conductivity of the epoxy resin conductive adhesive containing the composite conductive filler; the tight stacking structure is also conducive to improving the molecular cohesion of the conductive adhesive, thereby improving the bonding performance. Stearic acid is used to chemically coat the surface of the micron / nano composite silver powder to form a spatial isolation layer. The stearic acid molecules are bound 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 the silver powder particles and delay oxidation to improve its dispersibility and other properties. DETAILED DESCRIPTION

[0057] 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.

[0058] Example A1

[0059] 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 11 (weight percentage).

[0060] The preparation process of A1 is as follows:

[0061] (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.

[0062] (2) Prepare your own single-walled / multi-walled carbon nanotubes. Weigh single-walled carbon nanotubes and multi-walled carbon nanotubes in a weight ratio of 1:5.0 and mix them evenly to obtain single-walled / multi-walled carbon nanotubes. Set aside.

[0063] (3) Prepare epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes. Weigh single-walled / multi-walled composite carbon nanotubes, epoxy soybean oil, and acetone in a weight ratio of 1:1.25:4. Dissolve the epoxy soybean oil in acetone, then add the single-walled / multi-walled carbon nanotubes and stir evenly to obtain granular epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes. Set aside.

[0064] (4) Homemade carbon nanotube / carbon fiber conductive composite material. According to the components and their weight percentages specified in Table 1 for "Example A1," weigh the homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes, carbon fibers, an antioxidant, a lubricant, and a solvent, and mix them uniformly to obtain a homemade carbon nanotube / carbon fiber conductive composite material. Set aside.

[0065] (5) Pretreatment of silver powder: According to the components and weight percentages of "Example A1" specified in Table 1, nano-scale silver powder, micron-scale silver powder, and surface treatment agent stearic acid were weighed separately and stirred at a low speed of 300 r / min for 25 minutes to obtain pretreated silver powder.

[0066] (6) According to the components and their weight percentages of “Example A1” specified in Table 1, the homemade carbon nanotube / carbon fiber conductive composite material, pretreated silver powder, dispersant, and solvent were weighed, added to a mixing device, and stirred at a low speed for 25 minutes to obtain a first mixture.

[0067] (7) According to the components and weight percentages of “Example A1” specified in Table 1, the homemade graphene oxide-modified epoxy resin and coupling agent were weighed and added to the first mixture, and stirred at low speed for 15 minutes to obtain a second mixture.

[0068] (8) According to the components and weight percentages of "Example A1" specified in Table 1, weigh the curing agent and curing accelerator separately and add them to the second mixture. Stir at low speed for 10 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 produce a high thermal conductivity epoxy resin conductive adhesive containing a composite conductive filler.

[0069] Comparative Example B1

[0070] B1 is a technical solution using graphene-modified epoxy resin, and the amount of graphene-modified epoxy resin used is 11 (weight percentage).

[0071] The preparation process of B1 is as follows:

[0072] (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 admixture for 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.

[0073] (2) The rest of the experimental process is the same as steps (2) to (8) in Example 1.

[0074] Comparative Example C1

[0075] C1 is a technical solution using unmodified epoxy resin, and the amount of unmodified epoxy resin used is 11 (weight percentage).

[0076] The preparation process of C1 is as follows:

[0077] (1) Prepare 500 mL of epoxy resin E51 (density 1.16 g / ml). Set aside.

[0078] (2) The rest of the experimental process is the same as steps (2) to (8) in Example 1.

[0079] Example A2

[0080] A2 also utilizes graphene oxide-modified epoxy resin (the technology of this patent), but uses 8 weight percent of the graphene oxide-modified epoxy resin. The components of "Example A2" are weighed according to their weight percentages as specified in Table 1. Aside from the weight percentages of the components, the preparation method is otherwise identical to Example A1.

[0081] Example A3

[0082] 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 14% (by weight). 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.

[0083] Comparative Example B2

[0084] B2 is a technical solution using a graphene-modified epoxy resin, with the amount of graphene-modified epoxy resin being 8 (weight percent). The weights of the components of "Comparative Example B2" and their weight percentages specified in Table 1 were used to weigh the components. Compared to Example B1, except for the different weight percentages of the components, the preparation method was otherwise identical.

[0085] Comparative Example B3

[0086] B3 is a technical solution using a graphene-modified epoxy resin, with the amount of graphene-modified epoxy resin used being 14 (weight percent). The weights of the components of "Comparative Example B3" and their weight percentages specified in Table 1 were used to weigh the components. Compared to Example B1, except for the different weight percentages of the components, the preparation method was otherwise identical.

[0087] Comparative Example C2

[0088] C2 is a technical solution using unmodified epoxy resin, with the unmodified epoxy resin used in an amount of 8 weight percent. The components of "Comparative Example C2" were weighed according to their weight percentages specified in Table 1. The preparation method was identical to that of Example C1, except for the weight percentages of the components.

[0089] Comparative Example C3

[0090] C3 is a technical solution using unmodified epoxy resin, with the unmodified epoxy resin used in an amount of 14% by weight. The components of "Comparative Example C3" were weighed according to their weight percentages specified in Table 1. The preparation method was identical to that of Example C1, except for the different weight percentages of the components.

[0091] Comparative Example D

[0092] D is commercially available epoxy conductive silver glue.

[0093] Examples A1-A3, Comparative Examples B1-B3, and Comparative Examples C1-C3, prepared according to the present invention, and Comparative Example D, a similar commercial product, were sampled and tested for dispersion, thermal conductivity, electrical conductivity, and mechanical properties of the conductive adhesive. The thermal conductivity of the conductive adhesive was tested using an 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 according to the national standard GB / T 2567-2008. The test results are shown in Table 1.

[0094] Table 1 Effects of unmodified epoxy resin and epoxy resin modified by different methods on the properties of conductive adhesive

[0095]

[0096]

[0097] Comparing the data in Table 1 shows that the conductive adhesives 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 adhesives 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 have excellent thermal conductivity, with thermal conductivity coefficients (W / (m·K)) of 21.5, 21.1, and 21.8, respectively, which are higher than those of Comparative Examples B1-B3 (17.5, 16.5, and 18.3), and higher than those of Comparative Examples C1-C3 (15.5, 15.3, and 16.0), and higher than that of Comparative Example D (only 9.8), a similar product on the market.

[0099] Examples A1-A3 have excellent electrical conductivity, with volume resistivity (Ω·cm) of 0.3×10 -4 , 0.4×10 -4 , 0.2×10 -4 , which is significantly smaller than that of comparative examples B1-B3 (0.7×10 -4 , 0.8×10 -4 , 0.6×10 -4 ), which is also smaller than that of comparative examples C1-C3 (0.8×10 -4 , 0.9×10 -4 , 0.7×10 -4 ), which is much smaller than the comparative example D (2.3×10 -4 ).

[0100] 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 conductive adhesives (Examples A1-A3) produced using graphene oxide-modified epoxy resin technology achieved flexural strengths of 135 MPa, 139 MPa, and 130 MPa, respectively, and tensile strengths of 56 MPa, 61 MPa, and 52 MPa, respectively—significantly higher than the flexural strength (83 MPa) and tensile strength (35 MPa) of a similar commercial product, Comparative Example D.

[0101] In order to investigate the performance advantages of the surface modification of compounded single-walled / multi-walled carbon nanotubes using epoxy soybean oil according to the technical solution of the present invention, the following examples and comparative examples are compared for the conductive silver paste prepared by four schemes, namely, epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes (the method of this patent), epoxy soybean oil-modified single-walled carbon nanotubes, epoxy soybean oil-modified multi-walled carbon nanotubes, and unmodified single-walled / multi-walled carbon nanotubes, as well as commercially available epoxy resin conductive silver paste.

[0102] Example A4

[0103] A4 is a technical solution using epoxidized soybean oil to modify single-walled / multi-walled carbon nanotubes (method of this patent). The components of "Example A4" and their weight percentages are measured according to Table 2. The preparation process is the same as that of Example A1.

[0104] Comparative Example B4

[0105] B4 is a technical solution for modifying single-walled carbon nanotubes using epoxy soybean oil. The weights of the components of "Comparative Example B4" and their weight percentages specified in Table 2 were used to weigh the components.

[0106] The preparation process of B4 is as follows:

[0107] (1) Preparation of graphene oxide-modified epoxy resin: The same as step (1) of Example A1.

[0108] (2) Prepare epoxidized soybean oil-modified single-walled carbon nanotubes. Weigh single-walled carbon nanotubes, epoxidized soybean oil, and acetone in a weight ratio of 1:1.25:4. Dissolve the epoxidized soybean oil in acetone, then add the single-walled carbon nanotubes and stir evenly to obtain granular epoxidized soybean oil-modified single-walled carbon nanotubes. Set aside.

[0109] (3) Self-made carbon nanotube / carbon fiber conductive composite material. According to the components and weight percentages specified in "Comparative Example B4" in Table 2, weigh the self-made epoxidized soybean oil-modified single-walled carbon nanotubes, carbon fibers, an antioxidant, a lubricant, and a solvent, mix them uniformly, and obtain a self-made carbon nanotube / carbon fiber conductive composite material. Set aside.

[0110] (4) Pre-treat the silver powder, which is the same as step (5) of Example A1.

[0111] (5) Same as step (6) of Example A1.

[0112] (6) The same as step (7) of Example A1.

[0113] (7) The same as step (8) of Example A1.

[0114] Comparative Example C4

[0115] C4 is a technical solution for modifying multi-walled carbon nanotubes using epoxy soybean oil. The weights of the components of "Comparative Example C4" and their weight percentages specified in Table 2 were used to weigh the components.

[0116] The preparation process of C4 is as follows:

[0117] (1) Preparation of graphene oxide-modified epoxy resin: The same as step (1) of Example A1.

[0118] (2) Prepare homemade epoxidized soybean oil-modified multi-walled carbon nanotubes. Weigh multi-walled carbon nanotubes, epoxidized soybean oil, and acetone in a weight ratio of 1:1.25:4. Dissolve the epoxidized soybean oil in acetone, then add the multi-walled carbon nanotubes and stir evenly to obtain granular epoxidized soybean oil-modified multi-walled carbon nanotubes. Set aside.

[0119] (3) Self-made carbon nanotube / carbon fiber conductive composite material. According to the components and weight percentages of "Comparative Example C4" specified in Table 2, weigh the self-made epoxidized soybean oil-modified multi-walled carbon nanotubes, carbon fibers, antioxidant, lubricant, and solvent, mix them uniformly, and obtain a self-made carbon nanotube / carbon fiber conductive composite material. Set aside.

[0120] (4) Pre-treat the silver powder, which is the same as step (5) of Example A1.

[0121] (5) Same as step (6) of Example A1.

[0122] (6) The same as step (7) of Example A1.

[0123] (7) The same as step (8) of Example A1.

[0124] Comparative Example D4

[0125] D4 is a technical solution using unmodified single-walled / multi-walled carbon nanotubes. The weight of each component is weighed according to the components and weight percentages of "Comparative Example D4" specified in Table 2.

[0126] The preparation process of D4 is as follows:

[0127] (1) Preparation of graphene oxide-modified epoxy resin: The same as step (1) of Example A1.

[0128] (2) Self-made single-walled / multi-walled composite carbon nanotubes. The same as step (2) of Example A1.

[0129] (3) Self-made carbon nanotube / carbon fiber conductive composite material. According to the components and weight percentages of "Comparative Example B4" specified in Table 2, weigh the self-made single-walled / multi-walled composite carbon nanotubes, carbon fibers, antioxidant, lubricant, solvent, etc., and mix them evenly to obtain the self-made carbon nanotube / carbon fiber conductive composite material. Set aside.

[0130] (4) Pre-treat the silver powder, which is the same as step (5) of Example A1.

[0131] (5) Same as step (6) of Example A1.

[0132] (6) The same as step (7) of Example A1.

[0133] (7) The same as step (8) of Example A1.

[0134] Comparative Example E4

[0135] E4 is a commercially available epoxy resin conductive silver paste (the sample is the same as Comparative Example D).

[0136] Samples of Example A4, Comparative Example B4, Comparative Example C4, and Comparative Example D4 prepared according to the present invention, as well as Comparative Example E4, a similar commercial product, were prepared and tested for dispersion, thermal conductivity, electrical conductivity, and mechanical properties of the conductive adhesive. The thermal conductivity of the conductive adhesive was tested using an 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 according to the national standard GB / T 2567-2008. The test results are shown in Table 2.

[0137] Table 2 Effects of unmodified carbon nanotubes and modified single / multi-walled carbon nanotubes on the properties of conductive adhesives

[0138]

[0139]

[0140] Comparing the data in Table 2 shows that the conductive adhesive produced using the epoxy soybean oil-modified single-walled / multi-walled carbon nanotube technology (the method of this patent) (Example A4) exhibits uniform dispersion of conductive particles, with no agglomeration or precipitation. The conductive adhesives produced using the epoxy soybean oil-modified single-walled / multi-walled carbon nanotube technology (Comparative Example B4) and the epoxy soybean oil-modified multi-walled carbon nanotube technology (Comparative Example C4) exhibit good dispersion, with no significant agglomeration or precipitation. The conductive adhesive produced using unmodified single-walled / multi-walled carbon nanotubes (Comparative Example D4) exhibits uneven dispersion of conductive particles, with significant agglomeration or precipitation. The commercially available epoxy resin conductive silver adhesive (Comparative Example E4) exhibits good dispersion, with no significant agglomeration or precipitation.

[0141] Example A4 has excellent comprehensive performance, excellent thermal conductivity, and its thermal conductivity coefficient (W / (m·K) is 21.5; excellent electrical conductivity, and its volume resistivity (Ω·cm) is 0.3×10 -4 ; Excellent mechanical properties, its bending strength and tensile strength reach 135MPa and 56MPa respectively.

[0142] Compared with Example A4, the conductivity of Comparative Example B4 is improved, and the volume resistivity (Ω·cm) is only 0.2×10 -4 Its flexural strength and tensile strength are slightly improved, reaching 138 MPa and 59 MPa, respectively; however, its thermal conductivity is significantly lower than that of Example A4, with a thermal conductivity coefficient (W / (m·K)) of only 20.1.

[0143] The thermal conductivity of Comparative Example C4 is improved, with a thermal conductivity coefficient (W / (m·K)) as high as 21.9; its flexural strength and tensile strength are slightly reduced, to 130 MPa and 51 MPa respectively; however, its electrical conductivity is significantly lower than that of Example A4, with a volume resistivity (Ω·cm) as high as 0.5×10 -4 .

[0144] In the conductive adhesive of Comparative Example D4, the conductive particles are unevenly dispersed, with obvious agglomeration or precipitation. Its thermal conductivity, electrical conductivity, and mechanical properties are inferior to those of Example A4.

[0145] Compared with Example A4, the thermal conductivity, electrical conductivity and mechanical properties of the commercially available epoxy resin conductive silver paste (Comparative Example E4) are all inferior to those of Example A4.

[0146] In summary, the conductive adhesive (Example A4) prepared using the technology of epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes (the method of this patent) has excellent comprehensive performance and is the most optimal solution. The conductive adhesive (Comparative Example B4) prepared using the technology of epoxy soybean oil-modified single-walled carbon nanotubes (the method of this patent) has excellent electrical conductivity, but significantly lower thermal conductivity; the conductive adhesive (Comparative Example C4) prepared using the technology of epoxy soybean oil-modified multi-walled carbon nanotubes (the method of this patent) has excellent thermal conductivity, but significantly lower electrical conductivity. The conductive adhesive (Comparative Example D4) prepared using unmodified single-walled / multi-walled carbon nanotubes and the commercially available epoxy resin conductive silver adhesive (Comparative Example E4) are not as good as Example A4 in terms of thermal conductivity, electrical conductivity, and mechanical properties.

[0147] To investigate the effects of different weight ratios of single-walled / multi-walled carbon nanotubes modified with homemade epoxidized soybean oil to carbon fibers on the properties of the conductive adhesive according to the technical solution of the present invention, the properties of the conductive silver adhesives prepared using Example A5 (the preferred method of this patent), Example B5 (the general method of this patent), Example C5 (the general method of this patent), Comparative Example D5, Comparative Example E5, and Comparative Example F5 are compared and analyzed below.

[0148] Example A5

[0149] A5 utilizes homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes and carbon fibers in a weight ratio of 5:5 (the preferred method of this patent). The components of "Example A5" were weighed according to their weight percentages as specified in Table 3. The preparation process was the same as that of Example A1.

[0150] Example B5

[0151] B5 utilizes a 3:7 weight ratio of single-walled / multi-walled carbon nanotubes (SW / MWCNTs) modified with homemade epoxidized soybean oil to carbon fibers (the general method of this patent). The components of "Comparative Example B5" were weighed according to their weight percentages as specified in Table 3. The preparation process was identical to that of Example A5.

[0152] Example C5

[0153] C5 utilizes a 7:3 weight ratio of single-walled / multi-walled carbon nanotubes (SW / MWCNTs) modified with homemade epoxidized soybean oil to carbon fibers (the general method of this patent). The components of "Comparative Example C5" were weighed according to their weight percentages as specified in Table 3. The preparation process was identical to that of Example A5.

[0154] Comparative Example D5

[0155] D5 utilizes homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes (SW / MWCNTs) and carbon fibers in a 10:0 weight ratio. The components and their weight percentages for "Comparative Example D5" are measured according to Table 3. The preparation process is the same as that for Example A5.

[0156] Comparative Example E5

[0157] E5 utilizes homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes (SW / MWCNTs) and carbon fibers in a weight ratio of 0:10. The components of "Comparative Example E5" were weighed according to their weight percentages specified in Table 3. The preparation process was the same as in Example A5.

[0158] Comparative Example F5

[0159] F5 is a commercially available epoxy resin conductive silver paste (the sample is the same as Comparative Example D).

[0160] Samples of Example A5, Example B5, Example C5, Comparative Example D5, Comparative Example E5, and Comparative Example F5 prepared according to the present invention were prepared and tested for dispersion, thermal conductivity, electrical conductivity, and mechanical properties of the conductive adhesive. The thermal conductivity of the conductive adhesive was tested using an 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 according to the national standard GB / T 2567-2008. The test results are shown in Table 3.

[0161] Table 3 Effect of different weight ratios of homemade carbon nanotubes and carbon fibers on the properties of conductive adhesive

[0162]

[0163]

[0164] As shown in Table 3, when the weight ratio of the homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes to carbon fibers is 5:5 (the preferred method of this patent), the resulting conductive adhesive (Example A5) 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 21.5; and excellent electrical conductivity, with a volume resistivity (Ω·cm) of 0.3×10 -4 ; Excellent mechanical properties, its bending strength and tensile strength reach 135MPa and 56MPa respectively.

[0165] Compared with Example A5, Example B5, which uses a technical solution in which the weight ratio of single-walled / multi-walled carbon nanotubes / carbon fibers modified with homemade epoxidized soybean oil is 3:7 (the general method of this patent), is a better choice. Its flexural strength and tensile strength are slightly improved, reaching 146 MPa and 65 MPa, respectively; however, its thermal and electrical conductivity are both reduced, with the thermal conductivity coefficient (W / (m·K)) being only 20.9, and its volume resistivity (Ω·cm) increasing by 0.4×10 -4 .

[0166] Example C5, which uses a technical solution in which the weight ratio of single-walled / multi-walled carbon nanotubes modified with homemade epoxidized soybean oil to carbon fibers is 7:3 (the general method of this patent), is also a good choice. Compared with Example A5, its flexural strength and tensile strength are slightly improved, reaching 132 MPa and 52 MPa, respectively; however, its thermal and electrical conductivity are also somewhat reduced, with the thermal conductivity coefficient (W / (m·K)) being 21.2, and its volume resistivity (Ω·cm) increasing by 0.4×10 -4 .

[0167] In the technical solution of Comparative Example D5, the weight ratio of homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes to carbon fibers was 10:0, i.e., no carbon fibers were added. In the technical solution of Comparative Example E5, the weight ratio of homemade epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes to carbon fibers was 0:10, i.e., no modified carbon nanotubes were added. Therefore, the synergistic effect of carbon nanotubes and carbon fibers did not appear in the conductive adhesive systems of D5 and E5, and the conductive performance of the conductive adhesive was significantly reduced. The volume resistivity (Ω·cm) of Comparative Example D5 increased by 0.8×10 -4 In contrast, the volume resistivity (Ω·cm) of Comparative Example E5 increased by 1.2×10 -4 .

[0168] Compared with Example A5, the thermal conductivity, electrical conductivity and mechanical properties of the commercially available epoxy resin conductive silver paste (Comparative Example E4) are all inferior to those of Example A5.

[0169] In summary, the conductive adhesive prepared by the scheme of 5:5 using the weight ratio of homemade epoxy soybean oil modified single-walled / multi-walled carbon nanotubes and carbon fiber (Example A5, the preferred method of this patent) has the best overall performance and is the best technical solution. The scheme of 3:7 using the weight ratio of homemade epoxy soybean oil modified single-walled / multi-walled carbon nanotubes and carbon fiber (Example B5, the general method of this patent) and the scheme of 7:3 using the weight ratio of homemade epoxy soybean oil modified single-walled / multi-walled carbon nanotubes and carbon fiber (Example C5, the general method of this patent) have good overall performance. In comparative example D5, the weight ratio of homemade epoxy soybean oil modified single-walled / multi-walled carbon nanotubes and carbon fiber is 10:0, i.e., no carbon fiber is added; in comparative example E5, the weight ratio of homemade epoxy soybean oil modified single-walled / multi-walled carbon nanotubes and carbon fiber is 0:10, i.e., no modified carbon nanotubes are added. Therefore, the synergistic effect of carbon nanotubes and carbon fibers was not observed in the conductive adhesive systems D5 and E5, and the conductive performance of the conductive adhesives was significantly reduced, far inferior to that of Examples B5 and C5, and even inferior to that of Example A5. The thermal conductivity, electrical conductivity, and mechanical properties of the commercially available epoxy conductive silver adhesive (Comparative Example F4) were inferior to those of Examples A5, B5, and C5.

[0170] To investigate the effects of varying weight ratios of nano-silver powder to micron-silver powder and chemical coating treatment on the performance of the conductive adhesive, the following comparative analysis analyzes the performance of conductive silver adhesives prepared using Example A61 (the preferred method of this patent), Example A62 (the general method of this patent), Example A63 (the general method of this patent), Comparative Examples B61, C61, D61, B62, B63, and E6. Table 4 shows the formulation information and performance test results for each example and comparative example.

[0171] Example A61

[0172] A61 utilizes a composite of nanosilver powder and micronized silver powder in a weight ratio of 5:55, and chemically coats the surface of the micron / nanoscale composite silver powder with stearic acid (a preferred method in this patent). The components of "Example A61" and their weight percentages are measured according to Table 4. The preparation process is the same as that of Example A1.

[0173] Example A62

[0174] A62 utilizes a composite of nanosilver powder and micronized silver powder in a weight ratio of 4:56, 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 A62" are weighed according to their weight percentages as specified in Table 4. The preparation process is the same as that of Example A61.

[0175] Example A63

[0176] A63 utilizes a composite of nanosilver powder and micronized silver powder in a weight ratio of 6:54, 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 A63" are weighed according to their weight percentages as specified in Table 4. The preparation process is the same as that of Example A61.

[0177] Comparative Example B61

[0178] B61 utilizes a nanosilver powder to micron silver powder weight ratio of 5:55. In this comparative example, the surface treatment agent dosage is zero, meaning the silver powder is not subjected to surface chemical coating. The components and their weight percentages specified in Table 4 for "Example B61" were weighed. Aside from the lack of surface treatment on the silver powder, the remaining preparation process is identical to that of Example A61.

[0179] Comparative Example B62

[0180] B62 utilizes a nanosilver powder to micron silver powder weight ratio of 4:56. In this comparative solution, the surface treatment agent dosage is zero, meaning the silver powder is not subjected to surface chemical coating. The components and their weight percentages specified in Table 4 for "Example B62" were weighed. The preparation process is the same as that for Example B61.

[0181] Comparative Example B63

[0182] B63 utilizes a nanosilver powder to micron silver powder weight ratio of 6:54. 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 B63" and their weight percentages specified in Table 4 were weighed. The preparation process is the same as that of Example B61.

[0183] Comparative Example C61

[0184] C61 utilizes a 0:60 weight ratio of nanosilver powder to micronized silver powder, meaning all silver powder is micronized silver powder. The surface of the micronized silver powder is chemically coated with stearic acid. The components of "Example C61" are weighed according to their weight percentages specified in Table 4. The preparation process is the same as that of Example A61.

[0185] Comparative Example D61

[0186] D61 utilizes a 60:0 weight ratio of nanosilver powder to micronized silver powder, meaning all silver powder is nanosilver. The nanosilver powder is chemically coated with stearic acid. The components and their weight percentages for "Example D61" are measured according to Table 4. The preparation process is the same as that for Example A61.

[0187] Comparative Example E6

[0188] E6 is a commercially available epoxy resin conductive silver paste (the sample is the same as Comparative Example D).

[0189] Samples of Example A61, Example A62, Example A63, Comparative Example B61, Comparative Example C61, Comparative Example D61, Comparative Example B62, Comparative Example B63, and Comparative Example E6, prepared according to the present invention, were prepared and tested for dispersion, thermal conductivity, electrical conductivity, and mechanical properties of the conductive adhesive. The thermal conductivity of the conductive adhesive was tested using an 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 according to the national standard GB / T 2567-2008. The test results are shown in Table 4.

[0190] Table 4 Effect of chemical coating treatment on the surface of micro / nano silver powder on the performance of conductive adhesive

[0191]

[0192]

[0193] As shown in Table 4, when nano-silver powder and micron-silver powder are compounded at a weight ratio of 5:55 and the surface of the micron- / nano-scale composite silver powder is chemically coated with stearic acid (the preferred method of this patent), the resulting conductive adhesive (Example A61) 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 21.5; and excellent electrical conductivity, with a volume resistivity (Ω·cm) of 0.3×10 -4 ; Excellent mechanical properties, its bending strength and tensile strength reach 135MPa and 56MPa respectively.

[0194] Example A62 uses nano-silver powder and micron-silver powder in a weight ratio of 4:56, and uses stearic acid to chemically coat the surface of the micron- / nano-scale composite silver powder (the general method of this patent). Example A63 uses nano-silver powder and micron-silver powder in a weight ratio of 6:54, and uses stearic acid to chemically coat the surface of the micron- / nano-scale composite silver powder (the general method of this patent). Both are better technical solutions. The conductive particles of both are evenly dispersed, without agglomeration or precipitation. Both have excellent conductivity, the same as the test results of the A61 technical solution, and the volume resistivity (Ω·cm) is 0.3×10 -4 Compared with the technical solution of Example A61, the thermal conductivity, bending strength, and tensile strength of Examples A62 and A63 were slightly reduced, but the differences were not significant. Their thermal conductivity (W / (m·K)) was 20.8 and 21.2, respectively; their bending strength was 131 MPa and 133 MPa, respectively; and their tensile strength was 52 MPa and 54 MPa, respectively.

[0195] Comparative Examples B61, B62, and B63 all employed a technical solution in which nano-silver powder and micron-silver powder were compounded in a specific weight ratio, with the weight ratios being 5:55, 4:56, and 6:54, respectively. None of the compounded silver powders were chemically surface-coated with stearic acid. The experimental results in Table 4 demonstrate that the conductive particles of the three examples were unevenly dispersed, with significant agglomeration or precipitation. The agglomeration or precipitation of the conductive particles (particularly the composite silver powder) severely impacted the uniform distribution of the conductive particles within the conductive adhesive coating, leading to a sharp decrease in the thermal and electrical conductivity of the conductive adhesive. Compared to the technical solutions of Examples A61, A62, and A63, the flexural and tensile strengths of Comparative Examples B61, B62, and B63 also decreased significantly.

[0196] Comparative Example C61 employed a technical solution with a weight ratio of nano-silver powder to micron-silver powder of 0:60, meaning all silver powder used was micron-silver powder. D61 employed a technical solution with a weight ratio of nano-silver powder to micron-silver powder of 60:0, meaning all silver powder used was nano-silver powder. Both Comparative Examples C61 and D61 used stearic acid to chemically coat the silver powder surface. As shown in Table 4, the conductive particles in Comparative Example C61 were evenly dispersed, with no agglomeration or precipitation. Comparative Example C62 exhibited better dispersion, with no significant agglomeration or precipitation. Compared to the technical solution in Example A61, the thermal conductivity, electrical conductivity, flexural strength, and tensile strength of the conductive adhesive samples in Comparative Examples C61 and D61 decreased to a certain extent.

[0197] Compared with the technical solutions of Examples A61, A62 and A63, the thermal conductivity, electrical conductivity and mechanical properties of the commercially available epoxy resin conductive silver paste (Comparative Example E6) are all inferior to those of the examples.

[0198] In summary, by compounding nano-silver powder and micron-silver powder in a certain weight ratio and chemically coating the silver powder surface with stearic acid, an epoxy resin conductive adhesive with stable dispersion, good thermal conductivity, good electrical conductivity, and high bonding strength can be produced. When nano-silver powder and micron-silver powder are compounded, the nano-silver powder fills the intergranular spaces of the micron-silver powder, forming a tightly packed structure with the micron-silver powder. This can improve the thermal conductivity and electrical conductivity of the epoxy resin conductive adhesive, enhance the molecular cohesion of the conductive adhesive, and thereby enhance the flexural strength and tensile strength of the conductive adhesive. Chemically coating the composite silver powder surface with stearic acid can effectively reduce the agglomeration of the silver powder particles and delay their oxidation, thereby improving the dispersion and other properties of the composite silver powder.

[0199] 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 thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers, characterized in that: The invention comprises the following raw material components by weight percentage: 6-16% of graphene oxide modified epoxy resin, 0.6-3% of curing agent, 0-1% of curing accelerator, 2-7% of epoxy soybean oil modified single-layer / multi-layer carbon nanotubes, 3-7% of carbon fiber, 3-7% of nano-grade silver powder, 40-70% of micron-grade silver powder, 5.0-15.0% of surface treatment agent, 0.3-2.7% of coupling agent, 0.5-1.5% of dispersant, 0.1-0.3% of antioxidant, 0.1-0.5% of lubricant and the remainder of solvent.

2. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to claim 1, characterized in that: The graphene oxide modified epoxy resin is prepared by the following steps: Step 1: Prepare graphene oxide by a modified Hummers method: Graphite powder, concentrated sulfuric acid, and phosphoric acid are stirred and mixed in an ice-water bath, followed by the addition of KMnO4 and H2O2, followed by washing with hydrochloric acid solution and deionized water until neutral, and finally freeze-drying to obtain graphene oxide; Step 2, preparation of graphene oxide modified epoxy resin: preheat the epoxy resin to make it liquid, add graphene oxide to anhydrous ethanol, and ultrasonically disperse it; then pour the anhydrous ethanol solution of graphene oxide into the epoxy resin, ultrasonically disperse it, and after it is fully dispersed, stir while the epoxy resin remains liquid, then place it in a vacuum box, evacuate the air bubbles, and volatilize the anhydrous ethanol.

3. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to claim 2, characterized in that: In the step 1, KMnO4 and H2O2 are added slowly, and the concentration of the hydrochloric acid solution is 1-5%. The purity of the obtained graphene oxide is greater than 97wt%, the diameter is between 3-10μm, the number of layers is less than 5, and the thickness is 0.55-2.0nm. In the step 2, the epoxy resin is bisphenol A epoxy resin, bisphenol F epoxy resin, or 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 one of S-06E, TT21, and EP-4221-A; the preheating temperature of the epoxy resin is 60-80°C, and the preheating time is 20-40 minutes. in; the weight percentage of graphene oxide in epoxy resin is 0.1-1.0%; the volume ratio of anhydrous ethanol to epoxy resin is (2-3):1; the ultrasonic dispersion time of graphene oxide in anhydrous ethanol is 20-40 minutes; the ultrasonic dispersion time of the anhydrous ethanol solution of graphene oxide in the epoxy resin is 50-80 minutes, and the stirring is carried out in a water bath at 60-80° C. for 20-40 minutes; the temperature of the vacuum box is 78-90° C., and the vacuum is maintained for 1-3 hours.

4. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to any one of claims 1 to 3, characterized in that: The epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes are prepared by surface-modifying single-walled / multi-walled carbon nanotubes with epoxy soybean oil.

5. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to any one of claims 1 to 3, characterized in that: The epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes are prepared by the following steps: first dissolving the epoxidized soybean oil in acetone, then adding the single-walled / multi-walled carbon nanotubes, and stirring evenly to obtain granular epoxidized soybean oil-modified single-walled / multi-walled carbon nanotubes; The single-walled / multi-walled carbon nanotubes are compounded with single-walled carbon nanotubes and multi-walled carbon nanotubes in a weight ratio of 1:(2.0-8.0); The single-walled carbon nanotube has a diameter of 0.5 to 3 nm, a length of 1 to 50 μm, and an aspect ratio of 200 to 400,000; The multi-walled carbon nanotubes have a diameter of 10 to 60 nm, a length of 1 to 30 μm, and an aspect ratio of 1,000 to 1,000,000; The weight ratio of the single-layer / multi-layer carbon nanotubes, the epoxy soybean oil and the acetone is 1: (1.0～1.5):(3～5)。 6. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to any one of claims 1 to 3, characterized in that: The carbon fiber has an aspect ratio of 100 to 500, a diameter of 50 to 200 nm, and an aspect ratio of 30 to 300; The weight ratio of the carbon fibers to the epoxy soybean oil-modified single-walled / multi-walled carbon nanotubes is 3:7 to 7:3, preferably 1:

1.

7. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to any one of claims 1 to 3, characterized in that: The nano-scale silver powder and the micron-scale silver powder are coated with the surface treatment agent; The nano-scale silver powder and the micron-scale silver powder are compounded in a mass ratio of 1: (8.0-14.0); The nano-scale silver powder and the micron-scale silver powder constitute silver powder, and the weight ratio of the silver powder to the surface treatment agent is 1:(0.1-0.5); The particle size of the nano-scale silver powder can be at least one of 20 to 100 nm; the particle size of the micron-scale silver powder is 1 to 5 μm; The surface treatment agent is stearic acid.

8. The high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers 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 solvent is at least one of glycidyl ether, ethyl propionate, isobutyl formate, methyl propionate, butyl acetate, ethyl acetate, n-butyl acetate, isobutyl acetate, and n-butanol; The coupling agent is a silane coupling agent, and 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 dispersant is at least one of polyvinyl alcohol, sodium pyrophosphate, and sodium hexametaphosphate; The antioxidant is a compound of phenolic antioxidant 1010 and antioxidant 168 in a weight ratio of 1: (0.6-1.2); The lubricant is at least one of EBS, stearic acid, lauric acid, stearamide, and oleamide.

9. The method for preparing a high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Preparation of graphene oxide modified epoxy resin: Graphite powder, concentrated sulfuric acid and phosphoric acid are stirred and mixed in an ice-water bath, and then KMnO4 and H2O2 are added, followed by washing with hydrochloric acid solution and deionized water until neutral, and finally freeze-drying to obtain graphene oxide; the epoxy resin is preheated to make it liquid, and the graphene oxide is added to anhydrous ethanol and ultrasonically dispersed; then the anhydrous ethanol solution of graphene oxide is poured into the epoxy resin, ultrasonically dispersed, and after sufficient dispersion, stirred while the epoxy resin remains liquid, and then placed in a vacuum box, evacuated to degas, and the anhydrous ethanol is volatilized; S2. Preparing epoxidized soybean oil-modified single-wall / multi-wall carbon nanotubes: Weighing single-wall / multi-wall carbon nanotubes, epoxidized soybean oil, and acetone separately; dissolving the epoxidized soybean oil in acetone, then adding the single-wall / multi-wall carbon nanotubes, and stirring evenly to obtain granular epoxidized soybean oil-modified single-wall / multi-wall carbon nanotubes; S3. Weighing epoxy soybean oil-modified single-layer / multi-layer carbon nanotubes, carbon fibers, an antioxidant, a lubricant, and a portion of the solvent, respectively, and mixing them uniformly to obtain a carbon nanotube / carbon fiber conductive composite material; S4. Weigh nano-scale silver powder, micron-scale silver powder, and a surface treatment agent respectively, and stir to obtain pretreated silver powder; S5. Weigh the carbon nanotube / carbon fiber conductive composite material, pretreated silver powder, dispersant, and another portion of solvent, add them to a mixing device, and stir to obtain a first mixture; S6. Weighing graphene oxide-modified epoxy resin and coupling agent respectively, adding them to the first mixture, and stirring to obtain a second mixture; S7. Weigh the curing agent and curing accelerator separately, add them to the second mixture, stir, grind and disperse, and perform vacuum degassing to prepare a high thermal conductivity epoxy resin conductive adhesive containing composite conductive fillers.

10. The preparation method according to claim 9, characterized in that 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 in a three-roll mill until the conductive adhesive particles have a fineness not exceeding 5 μm.

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