Conductive graphite adhesive and preparation method thereof

Abstract

The present invention relates to the technical field of conductive adhesives, and in particular to a conductive graphite adhesive and a preparation method thereof. The conductive graphite adhesive is prepared by mixing bisphenol A epoxy resin, sulfonated bisphenol A epoxy resin, polyamide curing agent, dispersant, acetone, modified graphite, fumed silica and plasticizer. By introducing branched quaternary ammonium salt-modified graphite containing epoxy groups, the interfacial bonding force between graphite and matrix resin is significantly enhanced, and the electrical conductivity and mechanical properties are improved. In addition, the introduction of sulfonated bisphenol A epoxy resin improves the interfacial wettability between the matrix and graphite and enhances the corrosion resistance of the material. The conductive graphite adhesive of the present invention achieves comprehensive optimization in terms of electrical conductivity, mechanical properties and corrosion resistance, and is suitable for high-performance application scenarios such as electromagnetic shielding, electronic packaging and sensor devices.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive adhesives, in particular to a conductive graphite adhesive and a preparation method thereof. Background Art

[0002] With the rapid development of 5G communications, the Internet of Things, flexible electronics, and new energy vehicles, the comprehensive performance requirements of conductive materials have become increasingly stringent. Conductive graphite adhesive, a functional material that combines conductivity and processability, has broad application prospects in electromagnetic shielding, electronic packaging, sensor devices, and other fields. However, traditional conductive graphite adhesives have significant shortcomings in terms of interface compatibility, structural stability, and environmental adaptability, making it difficult to meet the requirements for material synergy optimization in high-performance scenarios.

[0003] With the trend towards miniaturization and integration of electronic components, the uniformity of dispersion and interfacial bonding strength of conductive fillers directly determine the conductive efficiency and mechanical reliability of the material. Graphite has become a mainstream filler due to its layered structure and high conductivity, but its flakes are easily agglomerated due to van der Waals forces, resulting in uneven dispersion. Existing technologies often use physical grinding or surfactant treatment to improve dispersibility, but such methods are difficult to form a stable chemically bonded interface. For example, although the use of silane coupling agents can improve the wettability of resins and fillers, excessive modification may lead to obstruction of the graphite conductive path; and although mechanical shear modification can temporarily disperse the particles, secondary agglomeration is prone to occur during the curing process, forming conductive network defects. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a conductive graphite adhesive and a preparation method thereof to solve the problems of poor graphite dispersion uniformity in existing conductive graphite adhesives and insufficient interface bonding strength between the conductive graphite adhesive and the resin matrix.

[0005] Based on the above objectives, the present invention provides a conductive graphite adhesive, which is prepared by mixing the following raw materials, in parts by weight: 120-140 parts of bisphenol A epoxy resin, 10-30 parts of sulfonated bisphenol A epoxy resin, 70-90 parts of polyamide curing agent, 20-30 parts of dispersant, 30-80 parts of acetone, 200-300 parts of modified graphite, 10-15 parts of fumed silica and 5-10 parts of plasticizer.

[0006] Furthermore, the sulfonated bisphenol A epoxy resin is obtained by sulfonating bisphenol A epoxy resin with fuming sulfuric acid and neutralizing it with sodium bicarbonate.

[0007] Preferably, the preparation method of the sulfonated bisphenol A epoxy resin is as follows: under a nitrogen atmosphere, bisphenol A epoxy resin is added to dichloromethane, stirred for 25-35 minutes, then anhydrous aluminum chloride is added, stirred for 8-12 minutes, and fuming sulfuric acid is added dropwise, the dropping rate is controlled so that the reaction temperature does not exceed 40°C, the temperature is raised to 60-70°C after the dropwise addition is completed, and the reaction is stirred for 3-5 hours. After the reaction is completed, the temperature is lowered to room temperature, poured into an ice-water mixture for quenching, and then sodium bicarbonate is added. The mixture is stirred for 20-40 minutes, dialyzed for purification, and vacuum dried to obtain the sulfonated bisphenol A epoxy resin. The weight ratio of the bisphenol A epoxy resin, dichloromethane, anhydrous aluminum chloride, fuming sulfuric acid, ice-water mixture and sodium bicarbonate is 10-30:50-200:0.2-0.6:10-20:100-300:10-30.

[0008] Preferably, the SO3 content of the fuming sulfuric acid is 20wt%-30wt%.

[0009] Preferably, the epoxy value of the bisphenol A epoxy resin is 0.48-0.56 mol / 100g.

[0010] Preferably, the amine value of the polyamide curing agent is 240-250 mgKOH / g.

[0011] Preferably, the dispersant is dispersant BYK-2150.

[0012] Preferably, the plasticizer is dioctyl phthalate.

[0013] Preferably, the specific surface area of ​​the fumed silica is 350-410 m 2 / g.

[0014] Furthermore, the preparation method of the modified graphite is as follows:

[0015] S1: Under a nitrogen atmosphere, epichlorohydrin and methanol were mixed, cooled to 8-12°C, 3-5 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 10-15 h, rotary evaporated, washed, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0016] S2: Add the diepoxy quaternary ammonium salt to deionized water, heat it to 35-45°C, stir it for 25-35 minutes, then add ethylenediamine and tris(2-aminoethyl)amine, heat it to 60-70°C, react it for 3-5 hours, wash it, and vacuum dry it to obtain a branched quaternary ammonium salt containing an epoxy group;

[0017] S3: Add flake graphite (particle size D50 is 8.5 μm) to deionized water, ultrasonicate for 20-40 minutes, then add branched quaternary ammonium salt containing epoxy group, heat to 75-85°C, stir for 5-7 hours, centrifuge, wash, and dry to obtain modified graphite.

[0018] Preferably, the particle size D50 of the flake graphite in step S3 is 6-10 μm.

[0019] Preferably, in step S1, the weight ratio of epichlorohydrin, methanol and N,N,N',N'-tetramethylethylenediamine is 19.9-29.9:4-6:3-5.

[0020] Preferably, in step S2, the weight ratio of the diepoxy quaternary ammonium salt, deionized water, ethylenediamine and tris(2-aminoethyl)amine is 21.4-35.6:150-200:1.8-3:0.6-1.

[0021] Preferably, in step S3, the weight ratio of flake graphite, deionized water and branched quaternary ammonium salt containing epoxy groups is 200-300:300-500:15-25.

[0022] Furthermore, the present invention provides a method for preparing a conductive graphite glue, comprising the following steps: mixing bisphenol A epoxy resin, sulfonated bisphenol A epoxy resin and polyamide curing agent, stirring at a speed of 300-500 rpm for 10-20 minutes, adding a dispersant and acetone, stirring at a speed of 700-900 rpm for 10-20 minutes, adding modified graphite, stirring at a speed of 1000-1500 rpm for 40-50 minutes at a vacuum degree of -0.095±0.002 MPa, then adding fumed silica and a plasticizer, stirring at a speed of 400-600 rpm for 25-35 minutes at a vacuum degree of -0.095±0.002 MPa to obtain a conductive graphite glue.

[0023] Beneficial effects of the present invention:

[0024] The conductive graphite adhesive of the present invention incorporates modified graphite with a branched quaternary ammonium salt containing epoxy groups, effectively enhancing the interfacial bonding between the graphite and the matrix resin, improving the material's electrical conductivity and mechanical properties. The unique structure of the branched quaternary ammonium salt containing epoxy groups forms a uniformly dispersed layer on the graphite surface and a uniform intercalated structure within the graphite, preventing graphite particle agglomeration and improving the uniformity and stability of the conductive network, resulting in the material's excellent electrical conductivity.

[0025] The branched quaternary ammonium salt-modified graphite containing epoxy groups provided by the present invention can undergo a cross-linking reaction with epoxy resin to construct a three-dimensional cross-linked network, thereby enhancing the material's ability to resist stress damage and significantly improving its mechanical properties, enabling it to withstand greater external force impacts.

[0026] The present invention improves the interfacial wettability between the resin matrix and the modified graphite by sulfonating the epoxy resin, and effectively enhances carrier mobility by cooperating with the modified graphite. Simultaneously, the sulfonic acid group can also form a charge shielding effect, reducing the damage of the environmental medium to the conductive network and improving the performance retention rate of the material in a corrosive environment. This balanced optimization in terms of conductivity, mechanical properties, and corrosion resistance makes the conductive graphite adhesive of the present invention suitable for a variety of application scenarios with high performance requirements. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0028] Example 1:

[0029] (1) Under nitrogen atmosphere, 17.9 g of epichlorohydrin and 4 g of methanol were mixed, cooled to 8°C, 3 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 10 h, rotary evaporated, washed with petroleum ether three times, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0030] (2) Add 21.4 g of diepoxy quaternary ammonium salt to 150 g of deionized water, heat to 35 ° C, stir for 25 min, then add 1.8 g of ethylenediamine and 0.6 g of tris(2-aminoethyl)amine, heat to 60 ° C, react for 3 h, wash with anhydrous ethanol three times, and vacuum dry to obtain a branched quaternary ammonium salt containing an epoxy group;

[0031] (3) 200 g of flake graphite (particle size D50 is 8.5 μm) was added to 300 g of deionized water, ultrasonicated for 20 min, and then 15 g of branched quaternary ammonium salt containing epoxy groups was added. The temperature was raised to 75 ° C. and stirred for 5 h. The mixture was centrifuged, washed, and dried to obtain modified graphite.

[0032] (4) Under nitrogen atmosphere, 10 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 50 g of dichloromethane and stirred for 25 min. Then, 0.2 g of anhydrous aluminum chloride was added and stirred for 8 min. Then, 10 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 60°C and stirred for 3 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 100 g of ice-water mixture for quenching. Then, 10 g of sodium bicarbonate was added and stirred for 20 min. The mixture was dialyzed for purification and dried in vacuo to obtain sulfonated bisphenol A epoxy resin.

[0033] (5) 120 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 10 g of sulfonated bisphenol A epoxy resin and 70 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 300 rpm for 10 min. 20 g of dispersant BYK-2150 and 30 g of acetone were added and stirred at 700 rpm for 10 min. 200 g of modified graphite was added and stirred at 1000 rpm for 40 min under a vacuum degree of -0.093 MPa. 10 g of fumed silica (specific surface area 380 m 2 / g) and 5g of dioctyl phthalate, and stirred at 400 rpm for 25 min under a vacuum degree of -0.093 MPa to obtain a conductive graphite glue.

[0034] Example 2:

[0035] (1) Under nitrogen atmosphere, 23.9 g of epichlorohydrin and 5 g of methanol were mixed, cooled to 10°C, 4 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 12 h, rotary evaporated, washed with petroleum ether three times, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0036] (2) Add 28.5 g of diepoxy quaternary ammonium salt to 170 g of deionized water, heat to 40 ° C, stir for 30 min, then add 2.4 g of ethylenediamine and 0.8 g of tris(2-aminoethyl)amine, heat to 65 ° C, react for 4 h, wash with anhydrous ethanol three times, and vacuum dry to obtain a branched quaternary ammonium salt containing an epoxy group;

[0037] (3) 250 g of flake graphite (particle size D50 is 8.5 μm) was added to 400 g of deionized water, ultrasonicated for 30 min, and then 20 g of branched quaternary ammonium salt containing epoxy groups was added. The temperature was raised to 80 ° C. and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain modified graphite.

[0038] (4) Under nitrogen atmosphere, 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 100 g of dichloromethane and stirred for 30 min. Then, 0.5 g of anhydrous aluminum chloride was added and stirred for 10 min. After that, 15 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 65°C and stirred for 4 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 200 g of ice-water mixture for quenching. Then, 20 g of sodium bicarbonate was added and stirred for 30 min. The mixture was dialyzed for purification and vacuum dried to obtain sulfonated bisphenol A epoxy resin.

[0039] (5) 130 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 20 g of sulfonated bisphenol A epoxy resin and 80 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 400 rpm for 15 min. 25 g of dispersant BYK-2150 and 50 g of acetone were added and stirred at 800 rpm for 15 min. 250 g of modified graphite was added and stirred at 1200 rpm for 45 min under a vacuum degree of -0.095 MPa. 12 g of fumed silica (specific surface area 380 m 2 / g) and 8g of dioctyl phthalate, and stirred at 500 rpm for 30 min under a vacuum degree of -0.095 MPa to obtain a conductive graphite glue.

[0040] Example 3:

[0041] (1) Under nitrogen atmosphere, 129.9 g of epichlorohydrin and 6 g of methanol were mixed, cooled to 12°C, 5 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 15 h, rotary evaporated, washed with petroleum ether three times, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0042] (2) Add 35.6 g of diepoxy quaternary ammonium salt to 200 g of deionized water, heat to 45 ° C, stir for 35 min, then add 3 g of ethylenediamine and 1 g of tris(2-aminoethyl)amine, heat to 70 ° C, react for 5 h, wash with anhydrous ethanol three times, and vacuum dry to obtain a branched quaternary ammonium salt containing an epoxy group;

[0043] (3) 300 g of flake graphite (particle size D50 is 8.5 μm) was added to 500 g of deionized water, ultrasonicated for 40 min, and then 25 g of branched quaternary ammonium salt containing epoxy groups was added. The temperature was raised to 85 ° C. and stirred for 7 h. The mixture was centrifuged, washed, and dried to obtain modified graphite.

[0044] (4) Under nitrogen atmosphere, 30 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 200 g of dichloromethane and stirred for 35 min. Then, 0.6 g of anhydrous aluminum chloride was added and stirred for 12 min. After that, 120 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 70°C and stirred for 5 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 300 g of ice-water mixture for quenching. Then, 30 g of sodium bicarbonate was added and stirred for 40 min. The mixture was dialyzed for purification and vacuum dried to obtain sulfonated bisphenol A epoxy resin.

[0045] (5) 140 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 30 g of sulfonated bisphenol A epoxy resin and 90 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 500 rpm for 20 min. 30 g of dispersant BYK-2150 and 80 g of acetone were added and stirred at 900 rpm for 20 min. 300 g of modified graphite was added and stirred at 1500 rpm for 50 min under a vacuum degree of -0.097 MPa. 15 g of fumed silica (specific surface area 380 m 2 / g) and 10g of dioctyl phthalate, and stirred at 600 rpm for 35 min under a vacuum degree of -0.097 MPa to obtain a conductive graphite glue.

[0046] Comparative Example 1:

[0047] The difference between Comparative Example 1 and Example 2 is that the branched quaternary ammonium salt containing an epoxy group in step (3) is replaced by a diepoxy quaternary ammonium salt;

[0048] The specific steps are as follows:

[0049] (1) Under nitrogen atmosphere, 23.9 g of epichlorohydrin and 5 g of methanol were mixed, cooled to 10°C, 4 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 12 h, rotary evaporated, washed with petroleum ether three times, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0050] (2) 250 g of flake graphite (particle size D50 is 8.5 μm) was added to 400 g of deionized water, ultrasonicated for 30 min, and then 20 g of diepoxy quaternary ammonium salt was added. The temperature was raised to 80 ° C. and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain modified graphite.

[0051] (3) Under nitrogen atmosphere, 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 100 g of dichloromethane and stirred for 30 min. Then, 0.5 g of anhydrous aluminum chloride was added and stirred for 10 min. After that, 15 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 65°C and stirred for 4 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 200 g of ice-water mixture for quenching. Then, 20 g of sodium bicarbonate was added and stirred for 30 min. The mixture was dialyzed for purification and vacuum dried to obtain sulfonated bisphenol A epoxy resin.

[0052] (4) 130 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 20 g of sulfonated bisphenol A epoxy resin and 80 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 400 rpm for 15 min. 25 g of dispersant BYK-2150 and 50 g of acetone were added and stirred at 800 rpm for 15 min. 250 g of modified graphite was added and stirred at 1200 rpm for 45 min under a vacuum degree of -0.095 MPa. 12 g of fumed silica (specific surface area 380 m 2 / g) and 8g of dioctyl phthalate, and stirred at 500 rpm for 30 min under a vacuum degree of -0.095 MPa to obtain a conductive graphite glue.

[0053] Comparative Example 2:

[0054] The difference between Comparative Example 2 and Example 2 is that tris(2-aminoethyl)amine in step (2) is replaced by ethylenediamine;

[0055] The specific steps are as follows:

[0056] (1) Under nitrogen atmosphere, 23.9 g of epichlorohydrin and 5 g of methanol were mixed, cooled to 10°C, 4 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 12 h, rotary evaporated, washed with petroleum ether three times, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0057] (2) Add 28.5 g of diepoxy quaternary ammonium salt to 170 g of deionized water, heat to 40 ° C, stir for 30 min, then add 2.9 g of ethylenediamine, heat to 65 ° C, react for 4 h, wash with anhydrous ethanol three times, and vacuum dry to obtain a quaternary ammonium salt containing an epoxy group;

[0058] (3) 250 g of flake graphite (particle size D50 is 8.5 μm) was added to 400 g of deionized water, ultrasonicated for 30 min, and then 20 g of quaternary ammonium salt containing epoxy groups was added. The temperature was raised to 80 ° C, stirred for 6 h, centrifuged, washed, and dried to obtain modified graphite;

[0059] (4) Under nitrogen atmosphere, 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 100 g of dichloromethane and stirred for 30 min. Then, 0.5 g of anhydrous aluminum chloride was added and stirred for 10 min. After that, 15 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 65°C and stirred for 4 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 200 g of ice-water mixture for quenching. Then, 20 g of sodium bicarbonate was added and stirred for 30 min. The mixture was dialyzed for purification and vacuum dried to obtain sulfonated bisphenol A epoxy resin.

[0060] (5) 130 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 20 g of sulfonated bisphenol A epoxy resin and 80 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 400 rpm for 15 min. 25 g of dispersant BYK-2150 and 50 g of acetone were added and stirred at 800 rpm for 15 min. 250 g of modified graphite was added and stirred at 1200 rpm for 45 min under a vacuum degree of -0.095 MPa. 12 g of fumed silica (specific surface area 380 m 2 / g) and 8g of dioctyl phthalate, and stirred at 500 rpm for 30 min under a vacuum degree of -0.095 MPa to obtain a conductive graphite glue.

[0061] Comparative Example 3:

[0062] The difference between Comparative Example 3 and Example 2 is that the branched quaternary ammonium salt containing an epoxy group in step (3) is replaced by 2,3-epoxypropyltrimethylammonium chloride;

[0063] The specific steps are as follows:

[0064] (1) 250 g of flake graphite (particle size D50 is 8.5 μm) was added to 400 g of deionized water, ultrasonicated for 30 min, and then 20 g of 2,3-epoxypropyltrimethylammonium chloride was added. The temperature was raised to 80 ° C, stirred for 6 h, centrifuged, washed, and dried to obtain modified graphite;

[0065] (2) Under nitrogen atmosphere, 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 100 g of dichloromethane and stirred for 30 min. Then, 0.5 g of anhydrous aluminum chloride was added and stirred for 10 min. After that, 15 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 65°C and stirred for 4 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 200 g of ice-water mixture for quenching. Then, 20 g of sodium bicarbonate was added and stirred for 30 min. The mixture was purified by dialysis and dried in vacuo to obtain sulfonated bisphenol A epoxy resin.

[0066] (3) 130 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 20 g of sulfonated bisphenol A epoxy resin and 80 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 400 rpm for 15 min. 25 g of dispersant BYK-2150 and 50 g of acetone were added and stirred at 800 rpm for 15 min. 250 g of modified graphite was added and stirred at 1200 rpm for 45 min under a vacuum degree of -0.095 MPa. 12 g of fumed silica (specific surface area 380 m2 / g) and 8g of dioctyl phthalate, and stirred at 500 rpm for 30 min under a vacuum degree of -0.095 MPa to obtain a conductive graphite glue.

[0067] Comparative Example 4:

[0068] The difference between Comparative Example 4 and Example 2 is that the modified graphite in step (5) is replaced by flake graphite;

[0069] The specific steps are as follows:

[0070] (1) Under nitrogen atmosphere, 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 100 g of dichloromethane and stirred for 30 min. Then, 0.5 g of anhydrous aluminum chloride was added and stirred for 10 min. After that, 15 g of fuming sulfuric acid (SO3 content 25 wt%) was added dropwise. The addition rate was controlled so that the reaction temperature did not exceed 40°C. After the addition was completed, the temperature was raised to 65°C and stirred for 4 h. After the reaction was completed, the temperature was lowered to room temperature and poured into 200 g of ice-water mixture for quenching. Then, 20 g of sodium bicarbonate was added and stirred for 30 min. The mixture was dialyzed for purification and vacuum dried to obtain sulfonated bisphenol A epoxy resin.

[0071] (2) 130 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g), 20 g of sulfonated bisphenol A epoxy resin and 80 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 400 rpm for 15 min. 25 g of dispersant BYK-2150 and 50 g of acetone were added and stirred at 800 rpm for 15 min. 250 g of flake graphite (particle size D50 is 8.5 μm) was added and stirred at 1200 rpm for 45 min under vacuum degree of -0.095 MPa. 12 g of fumed silica (specific surface area 380 m 2 / g) and 8g of dioctyl phthalate, and stirred at 500 rpm for 30 min under a vacuum degree of -0.095 MPa to obtain a conductive graphite glue.

[0072] Comparative Example 5:

[0073] The difference between Comparative Example 5 and Example 2 is that the sulfonated bisphenol A epoxy resin in step (5) is replaced by bisphenol A epoxy resin;

[0074] The specific steps are as follows:

[0075] (1) Under nitrogen atmosphere, 23.9 g of epichlorohydrin and 5 g of methanol were mixed, cooled to 10°C, 4 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 12 h, rotary evaporated, washed with petroleum ether three times, and vacuum dried to obtain a diepoxy quaternary ammonium salt;

[0076] (2) Add 28.5 g of diepoxy quaternary ammonium salt to 170 g of deionized water, heat to 40 ° C, stir for 30 min, then add 2.4 g of ethylenediamine and 0.8 g of tris(2-aminoethyl)amine, heat to 65 ° C, react for 4 h, wash with anhydrous ethanol three times, and vacuum dry to obtain a branched quaternary ammonium salt containing an epoxy group;

[0077] (3) 250 g of flake graphite (particle size D50 is 8.5 μm) was added to 400 g of deionized water, ultrasonicated for 30 min, and then 20 g of branched quaternary ammonium salt containing epoxy groups was added. The temperature was raised to 80 ° C. and stirred for 6 h. The mixture was centrifuged, washed, and dried to obtain modified graphite.

[0078] (4) 150 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) and 80 g of polyamide curing agent (amine value 245 mgKOH / g) were mixed and stirred at 400 rpm for 15 min. 25 g of dispersant BYK-2150 and 50 g of acetone were added and stirred at 800 rpm for 15 min. 250 g of modified graphite was added and stirred at 1200 rpm for 45 min under a vacuum degree of -0.095 MPa. 12 g of fumed silica (specific surface area 380 m 2 / g) and 8g of dioctyl phthalate, and stirred at 500 rpm for 30 min under a vacuum degree of -0.095 MPa to obtain a conductive graphite glue.

[0079] Performance testing:

[0080] Curing sample: The conductive graphite glue prepared in the embodiment and comparative example was injected into the mold and cured under gradient temperature: the first stage was allowed to stand at 50°C for 2 hours; the second stage was cured at 80°C for 1 hour; the third stage was cured at 120°C for 0.5 hours, and then naturally cooled to room temperature.

[0081] Volume resistivity: The test was conducted in accordance with GB / T 29417-2012. The volume resistivity was determined using the four-probe method. The specimens were cut into 20 mm × 20 mm × 2 mm pieces and measured using a four-probe tester at 23 ± ℃. The average value of three parallel tests was recorded. The results are shown in Table 1.

[0082] Adhesion: According to GB / T 5210-2006, an adhesion tester was used. After the specimen was bonded and cured to a 45# steel substrate, it was vertically stretched at a rate of 1 mm / min until failure. The maximum load at the interface failure was recorded. The results are shown in Table 1.

[0083] Tensile strength at break: According to GB / T 1040.1-2018, the tensile test was performed at a rate of 5 mm / min using an electronic universal testing machine, and the tensile strength at break was calculated. The results are shown in Table 1.

[0084] Impact strength: tested according to GB / T 1843-2008, using an cantilever beam impact tester, with a specimen notch depth of 2 mm and a pendulum energy of 5.5 J. Five valid data points were collected for each test, and the average value was taken. The results are shown in Table 1.

[0085] Corrosion resistance test: According to GB / T 1771-2007, a neutral salt spray test was conducted in a salt spray chamber. The specimen was tilted at 45° and continuously sprayed with 5wt% NaCl solution. The chamber temperature was maintained at 35±2°C. The specimen was removed from the test chamber after 240 hours of testing, rinsed with deionized water, and dried. The volume resistivity change rate was measured. Each set of data was the average of three parallel tests. The results are shown in Table 1.

[0086] Table 1 Performance test results

[0087]

[0088] Data Analysis:

[0089] As can be seen from the data of Example 1-3 in Table 1, the conductive graphite glue prepared by the present invention shows excellent comprehensive properties in terms of volume resistivity, adhesion, tensile strength at break, impact strength and corrosion resistance. This may be due to the introduction of branched quaternary ammonium salts containing epoxy groups in the preparation process, and its special molecular structure can effectively improve the interfacial bonding force between graphite and the matrix resin, thereby significantly improving the electrical conductivity and mechanical properties of the material. Simultaneously, the epoxy groups in the branched quaternary ammonium salts can cross-link with epoxy resin, further enhancing the structural stability and durability of the material. In addition, the branched structure of the branched quaternary ammonium salts may form an evenly dispersed layer and interlayer intercalation structure on the graphite surface, while improving the graphite interlayer spacing, avoiding the agglomeration phenomenon of graphite particles, thereby improving the uniformity and stability of the conductive network. This molecular design and interface control strategy make the conductive graphite glue of the present invention show excellent balance in multiple performance indicators, and is suitable for application scenarios with higher requirements for electrical conductivity and mechanical properties.

[0090] As can be seen from the data of Example 2 and Comparative Examples 1-4 in Table 1, the branched quaternary ammonium salt containing epoxy groups used in Example 2 has significant advantages in improving the performance of conductive graphite glue. Compared with linear structures, branched quaternary ammonium salts may produce more effective steric hindrance effects. Their multiple active sites form multi-point anchoring with the graphite surface, enhancing interfacial bonding strength. The branched topological structure is conducive to forming a more uniform intercalation modification, expanding the distance between graphite layers while maintaining structural stability. This molecular design may reduce contact resistance by enhancing the π-electron delocalization effect, while the three-dimensional cross-linked network improves resistance to stress damage.

[0091] The data from Example 2 and Comparative Example 5 in Table 1 demonstrate that the sulfonated bisphenol A epoxy resin used in Example 2 offers significant advantages in improving the performance of the conductive graphite adhesive. The introduction of sulfonic acid groups likely enhances carrier mobility through a proton conduction mechanism, while their strong polarity improves interfacial wettability between the resin matrix and the filler. The combination of sulfonated epoxy resin and modified graphite not only enhances the stability of the conductive pathway but also reduces environmental damage to the conductive network through a charge-shielding effect, significantly improving the material's performance retention in corrosive environments.

[0092] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

Claims

1. A conductive graphite adhesive, characterized in that: The invention is prepared by mixing the following raw materials in parts by weight: 120-140 parts of bisphenol A epoxy resin, 10-30 parts of sulfonated bisphenol A epoxy resin, 70-90 parts of polyamide curing agent, 20-30 parts of dispersant, 30-80 parts of acetone, 200-300 parts of modified graphite, 10-15 parts of fumed silica and 5-10 parts of plasticizer; The sulfonated bisphenol A epoxy resin is obtained by sulfonating bisphenol A epoxy resin with fuming sulfuric acid and neutralizing it with sodium bicarbonate; The preparation method of the modified graphite is as follows: S1: Under a nitrogen atmosphere, epichlorohydrin and methanol were mixed, cooled to 8-12°C, 3-5 g of N,N,N',N'-tetramethylethylenediamine was added dropwise, stirred for 10-15 h, rotary evaporated, washed, and vacuum dried to obtain a diepoxy quaternary ammonium salt; S2: Add the diepoxy quaternary ammonium salt to deionized water, heat it to 35-45°C, stir it for 25-35 minutes, then add ethylenediamine and tris(2-aminoethyl)amine, heat it to 60-70°C, react it for 3-5 hours, wash it, and vacuum dry it to obtain a branched quaternary ammonium salt containing an epoxy group; S3: adding flake graphite to deionized water, ultrasonicating for 20-40 min, then adding branched quaternary ammonium salt containing epoxy group, heating to 75-85°C, stirring for 5-7 h, centrifuging, washing, and drying to obtain modified graphite; In step S1, the weight ratio of epichlorohydrin, methanol and N,N,N',N'-tetramethylethylenediamine is 19.9-29.9:4-6:3-5; In step S2, the weight ratio of the diepoxy quaternary ammonium salt, deionized water, ethylenediamine, and tris(2-aminoethyl)amine is 21.4-35.6:150-200:1.8-3:0.6-1; In step S3, the weight ratio of flake graphite, deionized water and branched quaternary ammonium salt containing epoxy group is 200-300:300-500:15-25; The preparation method of the sulfonated bisphenol A epoxy resin is as follows: under a nitrogen atmosphere, bisphenol A epoxy resin is added to dichloromethane, stirred for 25-35 minutes, anhydrous aluminum chloride is added, stirred for 8-12 minutes, and fuming sulfuric acid is added dropwise, the dropping speed is controlled so that the reaction temperature does not exceed 40° C. After the dropwise addition is completed, the temperature is raised to 60-70° C., stirred and reacted for 3-5 hours, and after the reaction is completed, the temperature is lowered to room temperature, poured into an ice-water mixture for quenching, and sodium bicarbonate is added, stirred for 20-40 minutes, dialyzed for purification, and vacuum dried to obtain the sulfonated bisphenol A epoxy resin.

2. The conductive graphite paste according to claim 1, characterized in that In the process of preparing the sulfonated bisphenol A epoxy resin, the weight ratio of bisphenol A epoxy resin, dichloromethane, anhydrous aluminum chloride, fuming sulfuric acid, ice-water mixture and sodium bicarbonate is 10-30:50-200:0.2-0.6:10-20:100-300:10-30.

3. The conductive graphite paste according to claim 1, characterized in that The SO3 content of the fuming sulfuric acid is 20wt%-30wt%.

4. The conductive graphite paste according to claim 1, characterized in that The epoxy value of the bisphenol A epoxy resin is 0.48-0.56 mol / 100 g, and the amine value of the polyamide curing agent is 240-250 mgKOH / g.

5. The conductive graphite paste according to claim 1, characterized in that: The dispersant is dispersant BYK-2150, and the plasticizer is dioctyl phthalate.

6. The conductive graphite paste according to claim 1, characterized in that The specific surface area of ​​the fumed silica is 350-410 m 2 / g.

7. The conductive graphite paste according to claim 1, characterized in that The particle size D50 of the flake graphite in step S3 is 6-10 μm.

8. A method for preparing a conductive graphite paste according to any one of claims 1 to 7, characterized in that: The following steps are involved: Bisphenol A epoxy resin, sulfonated bisphenol A epoxy resin and polyamide curing agent are mixed, stirred at a speed of 300-500 rpm for 10-20 minutes, and then a dispersant and acetone are added, and stirred at a speed of 700-900 rpm for 10-20 minutes. Then, modified graphite is added, and stirred at a speed of 1000-1500 rpm for 40-50 minutes under a vacuum degree of -0.095±0.002 MPa. Then, fumed silica and plasticizer are added, and stirred at a speed of 400-600 rpm for 25-35 minutes under a vacuum degree of -0.095±0.002 MPa to obtain a conductive graphite glue.

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