Conductive graphite adhesive and preparation method thereof

Abstract

The invention relates to the technical field of conductive adhesives, 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, a polyamide curing agent, a dispersing agent, acetone, modified graphite, fumed silica and a plasticizer. By introducing the branched quaternary ammonium salt modified graphite containing the epoxy group, the interface bonding force between the graphite and matrix resin is remarkably enhanced, and the conductivity and the mechanical property are improved. In addition, due to introduction of sulfonated bisphenol A epoxy resin, the interface wettability of a matrix and graphite is improved, and the corrosion resistance of the material is improved. The conductive graphite adhesive disclosed by the invention realizes comprehensive optimization in the aspects of conductivity, mechanical property, corrosion resistance and the like, and is suitable for high-performance application scenes such as electromagnetic shielding, electronic packaging, sensing devices and the like.

Description

Technical Field

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

[0002] With the rapid development of fields such as 5G communication, Internet of Things, flexible electronics, and new energy vehicles, the comprehensive performance requirements of conductive materials show multi-dimensional and stringent requirements. As a functional material with both conductivity and processability, conductive graphite adhesives have broad application prospects in fields such as electromagnetic shielding, electronic packaging, and sensor devices. However, traditional conductive graphite adhesives have significant shortcomings in aspects such as interfacial compatibility, structural stability, and environmental adaptability, and it is difficult to meet the requirements of high-performance scenarios for the collaborative optimization of materials.

[0003] In the trend of miniaturization and integration of electronic components, the dispersion uniformity and interfacial bonding strength of conductive fillers directly determine the conductive efficiency and mechanical reliability of the materials. Graphite has become the mainstream filler due to its layered structure and high conductivity, but its flakes are prone to agglomeration due to van der Waals forces, resulting in uneven dispersion. Existing technologies mostly use physical grinding or surfactant treatment to improve dispersion, but these methods are difficult to form a stable chemical bonding interface. For example, although the use of silane coupling agents can improve the wettability between the resin and the filler, it may cause the conductive path of graphite to be blocked due to excessive modification; while mechanical shear modification can temporarily disperse the particles, but it is prone to secondary agglomeration during the curing process, forming defects in the conductive network. 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 dispersion uniformity of graphite and insufficient interfacial bonding force between the conductive graphite adhesive and the resin matrix in the existing conductive graphite adhesives.

[0005] Based on the above purpose, 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] Further, the sulfonated bisphenol A epoxy resin is obtained by sulfonating bisphenol A epoxy resin with fuming sulfuric acid and neutralizing with sodium bicarbonate.

[0007] Preferably, the preparation method of the sulfonated bisphenol A epoxy resin is as follows: Under a nitrogen atmosphere, add bisphenol A epoxy resin to dichloromethane, stir for 25 - 35 min, then add anhydrous aluminum chloride, stir for 8 - 12 min, and then dropwise add fuming sulfuric acid. Control the dropping rate so that the reaction temperature does not exceed 40 °C. After the dropping is completed, raise the temperature to 60 - 70 °C, stir and react for 3 - 5 h. After the reaction is completed, cool down to room temperature, pour it into an ice - water mixture for quenching, then add sodium bicarbonate, stir for 20 - 40 min, purify by dialysis, and dry in vacuum to obtain 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.

[0008] Preferably, the SO 3 content of the fuming sulfuric acid is 20 wt% - 30 wt%.

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

[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, mix epichlorohydrin and methanol, cool down to 8 - 12 °C, dropwise add 3 - 5 g of N,N,N',N'-tetramethylethylenediamine, stir for 10 - 15 h, rotary evaporate, wash, and dry in vacuum to obtain bis - epoxy - quaternary ammonium salt;

[0016] S2: Add the bis - epoxy - quaternary ammonium salt to deionized water, raise the temperature to 35 - 45 °C, stir for 25 - 35 min, then add ethylenediamine and tris(2 - aminoethyl)amine, raise the temperature to 60 - 70 °C, react for 3 - 5 h, wash, and dry in vacuum to obtain a branched quaternary ammonium salt containing epoxy groups;

[0017] S3: Add flake graphite (with a particle size D50 of 8.5 μm) into deionized water, sonicate for 20 - 40 min, then add a branched quaternary ammonium salt containing epoxy groups, heat up to 75 - 85 °C, stir for 5 - 7 h, centrifuge, wash, and dry to obtain modified graphite.

[0018] Preferably, in step S3, the particle size D50 of the flake graphite 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 bis-epoxy 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 the flake graphite, deionized water, and the 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 adhesive, which includes the following steps: Mix bisphenol A epoxy resin, sulfonated bisphenol A epoxy resin, and polyamide curing agent, stir at a speed of 300 - 500 rpm for 10 - 20 min, then add a dispersant and acetone, stir at a speed of 700 - 900 rpm for 10 - 20 min, then add modified graphite, stir at a speed of 1000 - 1500 rpm for 40 - 50 min under a vacuum of -0.095 ± 0.002 MPa, then add fumed silica and a plasticizer, and stir at 400 - 600 rpm for 25 - 35 min under a vacuum of -0.095 ± 0.002 MPa to obtain the conductive graphite adhesive.

[0023] The beneficial effects of the present invention:

[0024] The conductive graphite adhesive of the present invention introduces a branched quaternary ammonium salt containing epoxy groups to modify graphite, effectively enhancing the interfacial bonding force between graphite and the matrix resin, and improving the electrical conductivity and mechanical properties of the material. The special structure of the branched quaternary ammonium salt containing epoxy groups forms a uniform dispersion layer on the surface of graphite and a uniform intercalation structure inside, avoiding the agglomeration of graphite particles, improving the uniformity and stability of the conductive network, and making the material perform excellently in electrical conductivity.

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

[0026] By sulfonating epoxy resin, the present invention improves the interfacial wettability between the resin matrix and modified graphite. Moreover, in combination with modified graphite, the carrier mobility is effectively enhanced. At the same time, the sulfonic acid groups 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, corrosion resistance, etc. makes the conductive graphite glue of the present invention applicable to various application scenarios with high performance requirements. Specific Embodiments

[0027] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the present invention in conjunction with specific embodiments.

[0028] Example 1:

[0029] (1) Under a 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 3 times with petroleum ether, and dried in vacuo to obtain a bis-epoxy quaternary ammonium salt;

[0030] (2) 21.4 g of the bis-epoxy quaternary ammonium salt was added to 150 g of deionized water, heated to 35 °C, stirred for 25 min, then 1.8 g of ethylenediamine and 0.6 g of tris(2-aminoethyl)amine were added, heated to 60 °C, reacted for 3 h, washed 3 times with absolute ethanol, and dried in vacuo to obtain a branched quaternary ammonium salt containing epoxy groups;

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

[0032] (4) Under a nitrogen atmosphere, 10 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) was added to 50 g of dichloromethane, stirred for 25 min, then 0.2 g of anhydrous aluminum chloride was added, stirred for 8 min, and then 10 g of fuming sulfuric acid (SO 3 content is 25 wt%) was added dropwise, controlling the dropping rate so that the reaction temperature does not exceed 40 °C. After the dropping was completed, the temperature was raised to 60 °C, stirred and reacted for 3 h. After the reaction ended, it was cooled to room temperature, poured into 100 g of an ice-water mixture for quenching, then 10 g of sodium bicarbonate was added, stirred for 20 min, dialyzed and purified, and dried in vacuo to obtain sulfonated bisphenol A epoxy resin;

[0033] (5) Mix 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), stir at a speed of 300 rpm for 10 min, then add 20 g of dispersant BYK-2150 and 30 g of acetone, stir at a speed of 700 rpm for 10 min, then add 200 g of modified graphite, stir at a speed of 1000 rpm for 40 min under a vacuum of -0.093 MPa, then add 10 g of fumed silica (specific surface area 380 m 2 / g) and 5 g of dioctyl phthalate, stir at 400 rpm for 25 min under a vacuum of -0.093 MPa to obtain electrically conductive graphite glue.

[0034] Example 2:

[0035] (1) Under a nitrogen atmosphere, mix 23.9 g of epichlorohydrin and 5 g of methanol, cool down to 10 °C, dropwise add 4 g of N,N,N',N'-tetramethylethylenediamine, stir for 12 h, rotary evaporate, wash with petroleum ether 3 times, and vacuum dry to obtain bis-epoxy quaternary ammonium salt;

[0036] (2) Add 28.5 g of bis-epoxy quaternary ammonium salt to 170 g of deionized water, heat up to 40 °C, stir for 30 min, then add 2.4 g of ethylenediamine and 0.8 g of tris(2-aminoethyl)amine, heat up to 65 °C, react for 4 h, wash with absolute ethanol 3 times, and vacuum dry to obtain a branched quaternary ammonium salt containing epoxy groups;

[0037] (3) Add 250 g of flake graphite (particle size D50 is 8.5 μm) to 400 g of deionized water, ultrasonicate for 30 min, then add 20 g of the branched quaternary ammonium salt containing epoxy groups, heat up to 80 °C, stir for 6 h, centrifuge, wash, and dry to obtain modified graphite;

[0038] (4) Under a nitrogen atmosphere, add 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) to 100 g of dichloromethane, stir for 30 min, then add 0.5 g of anhydrous aluminum chloride, stir for 10 min and then dropwise add 15 g of fuming sulfuric acid (SO 3 content is 25 wt%), control the dropping rate so that the reaction temperature does not exceed 40 °C, after dropping, heat up to 65 °C, stir and react for 4 h, after the reaction is completed, cool down to room temperature, pour into 200 g of ice-water mixture for quenching, then add 20 g of sodium bicarbonate, stir for 30 min, dialyze and purify, and vacuum dry to obtain sulfonated bisphenol A epoxy resin;

[0039] (5) Mix 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 mg KOH / g), stir at a speed of 400 rpm for 15 min, then add 25 g of dispersant BYK-2150 and 50 g of acetone, stir at a speed of 800 rpm for 15 min, then add 250 g of modified graphite, stir at a speed of 1200 rpm for 45 min under a vacuum of -0.095 MPa, then add 12 g of fumed silica (specific surface area 380 m 2 / g) and 8 g of dioctyl phthalate, stir at 500 rpm for 30 min under a vacuum of -0.095 MPa to obtain conductive graphite glue.

[0040] Example 3:

[0041] (1) Under a nitrogen atmosphere, mix 129.9 g of epichlorohydrin and 6 g of methanol, cool down to 12 °C, dropwise add 5 g of N,N,N',N'-tetramethylethylenediamine, stir for 15 h, perform rotary evaporation, wash with petroleum ether 3 times, and dry under vacuum to obtain bis-epoxy quaternary ammonium salt;

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

[0043] (3) Add 300 g of flake graphite (particle size D50 is 8.5 μm) to 500 g of deionized water, ultrasonicate for 40 min, then add 25 g of branched quaternary ammonium salt containing epoxy groups, heat up to 85 °C, stir for 7 h, centrifuge, wash, and dry to obtain modified graphite;

[0044] (4) Under a nitrogen atmosphere, add 30 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) to 200 g of dichloromethane, stir for 35 min, then add 00.6 g of anhydrous aluminum chloride, stir for 12 min and then dropwise add 120 g of fuming sulfuric acid (SO 3 content is 25 wt%), control the dropping rate so that the reaction temperature does not exceed 40 °C, after dropping, heat up to 70 °C, stir and react for 5 h, after the reaction, cool down to room temperature, pour into 300 g of ice-water mixture for quenching, then add 30 g of sodium bicarbonate, stir for 40 min, purify by dialysis, and dry under vacuum to obtain sulfonated bisphenol A epoxy resin;

[0045] (5) Mix 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 mg KOH / g), stir at a speed of 500 rpm for 20 min, then add 30 g of dispersant BYK-2150 and 80 g of acetone, stir at a speed of 900 rpm for 20 min, then add 300 g of modified graphite, stir at a speed of 1500 rpm for 50 min under a vacuum of -0.097 MPa, then add 15 g of fumed silica (specific surface area 380 m 2 / g) and 10 g of dioctyl phthalate, stir at 600 rpm for 35 min under a vacuum of -0.097 MPa to obtain electrically 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 epoxy groups in step (3) is replaced with a dicycloepoxy quaternary ammonium salt;

[0048] The specific steps are as follows:

[0049] (1) Under a nitrogen atmosphere, mix 23.9 g of epichlorohydrin and 5 g of methanol, cool down to 10 °C, dropwise add 4 g of N,N,N',N'-tetramethylethylenediamine, stir for 12 h, perform rotary evaporation, wash with petroleum ether 3 times, and dry under vacuum to obtain a dicycloepoxy quaternary ammonium salt;

[0050] (2) Add 250 g of flake graphite (particle size D50 is 8.5 μm) to 400 g of deionized water, ultrasonicate for 30 min, then add 20 g of dicycloepoxy quaternary ammonium salt, heat up to 80 °C, stir for 6 h, centrifuge, wash, and dry to obtain modified graphite;

[0051] (3) Under a nitrogen atmosphere, add 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) to 100 g of dichloromethane, stir for 30 min, then add 0.5 g of anhydrous aluminum chloride, stir for 10 min and then dropwise add 15 g of fuming sulfuric acid (SO 3 content is 25 wt%), control the dropping rate so that the reaction temperature does not exceed 40 °C, after dropping, heat up to 65 °C, stir and react for 4 h, after the reaction ends, cool down to room temperature, pour into 200 g of ice-water mixture for quenching, then add 20 g of sodium bicarbonate, stir for 30 min, perform dialysis purification, and dry under vacuum to obtain sulfonated bisphenol A epoxy resin;

[0052] (4) Mix 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 mg KOH / g), stir at a speed of 400 rpm for 15 min, then add 25 g of dispersant BYK-2150 and 50 g of acetone, stir at a speed of 800 rpm for 15 min, then add 250 g of modified graphite, stir at a speed of 1200 rpm for 45 min under a vacuum of -0.095 MPa, then add 12 g of fumed silica (specific surface area 380 m 2 / g) and 8 g of dioctyl phthalate, stir at 500 rpm for 30 min under a vacuum of -0.095 MPa to obtain 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 with ethylenediamine;

[0055] The specific steps are as follows:

[0056] (1) Under a nitrogen atmosphere, mix 23.9 g of epichlorohydrin and 5 g of methanol, cool down to 10 °C, dropwise add 4 g of N,N,N',N'-tetramethylethylenediamine, stir for 12 h, rotary evaporate, wash 3 times with petroleum ether, and vacuum dry to obtain bis-epoxy quaternary ammonium salt;

[0057] (2) Add 28.5 g of bis-epoxy quaternary ammonium salt to 170 g of deionized water, heat up to 40 °C, stir for 30 min, then add 2.9 g of ethylenediamine, heat up to 65 °C, react for 4 h, wash 3 times with absolute ethanol, and vacuum dry to obtain a quaternary ammonium salt containing epoxy groups;

[0058] (3) Add 250 g of flake graphite (particle size D50 is 8.5 μm) to 400 g of deionized water, ultrasonicate for 30 min, then add 20 g of quaternary ammonium salt containing epoxy groups, heat up to 80 °C, stir for 6 h, centrifuge, wash, and dry to obtain modified graphite;

[0059] (4) Under a nitrogen atmosphere, add 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) to 100 g of dichloromethane, stir for 30 min, then add 0.5 g of anhydrous aluminum chloride, stir for 10 min and then dropwise add 15 g of fuming sulfuric acid (SO 3 content is 25 wt%), control the dropping rate so that the reaction temperature does not exceed 40 °C, after dropping, heat up to 65 °C, stir and react for 4 h, after the reaction is completed, cool down to room temperature, pour into 200 g of ice-water mixture for quenching, then add 20 g of sodium bicarbonate, stir for 30 min, dialyze and purify, and vacuum dry to obtain sulfonated bisphenol A epoxy resin;

[0060] (5) Mix 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 mg KOH / g), stir at a speed of 400 rpm for 15 min, then add 25 g of dispersant BYK-2150 and 50 g of acetone, stir at a speed of 800 rpm for 15 min, then add 250 g of modified graphite, stir at a speed of 1200 rpm for 45 min under a vacuum of -0.095 MPa, then add 12 g of fumed silica (specific surface area 380 m 2 / g) and 8 g of dioctyl phthalate, stir at 500 rpm for 30 min under a vacuum of -0.095 MPa to obtain conductive graphite glue.

[0061] Comparative Example 3:

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

[0063] The specific steps are as follows:

[0064] (1) Add 250 g of flake graphite (particle size D50 is 8.5 μm) to 400 g of deionized water, ultrasonicate for 30 min, then add 20 g of 2,3-epoxypropyltrimethylammonium chloride, heat up to 80 °C, stir for 6 h, centrifuge, wash, and dry to obtain modified graphite;

[0065] (2) Under a nitrogen atmosphere, add 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) to 100 g of dichloromethane, stir for 30 min, then add 0.5 g of anhydrous aluminum chloride, stir for 10 min and then dropwise add 15 g of fuming sulfuric acid (SO 3 content is 25 wt%), control the dropping rate so that the reaction temperature does not exceed 40 °C, after dropping, heat up to 65 °C, stir and react for 4 h, after the reaction ends, cool down to room temperature, pour into 200 g of ice-water mixture for quenching, then add 20 g of sodium bicarbonate, stir for 30 min, dialyze and purify, and vacuum dry to obtain sulfonated bisphenol A epoxy resin;

[0066] (3) Mix 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), stir at a speed of 400 rpm for 15 min, then add 25 g of dispersant BYK-2150 and 50 g of acetone, stir at a speed of 800 rpm for 15 min, then add 250 g of modified graphite, stir at a speed of 1200 rpm for 45 min under a vacuum of -0.095 MPa, then add 12 g of fumed silica (specific surface area 380 m 2 / g) and 8 g of dioctyl phthalate, stir at 500 rpm for 30 min under a vacuum of -0.095 MPa to obtain 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 with flake graphite;

[0069] The specific steps are as follows:

[0070] (1) Under a nitrogen atmosphere, add 20 g of bisphenol A epoxy resin (epoxy value 0.52 mol / 100 g) to 100 g of dichloromethane, stir for 30 min, then add 0.5 g of anhydrous aluminum chloride, stir for 10 min and then dropwise add 15 g of fuming sulfuric acid (SO 3 content is 25 wt%), control the dropping rate so that the reaction temperature does not exceed 40 °C, after dropping, raise the temperature to 65 °C, stir and react for 4 h, after the reaction ends, cool to room temperature, pour into 200 g of ice-water mixture for quenching, then add 20 g of sodium bicarbonate, stir for 30 min, dialyze and purify, vacuum dry to obtain sulfonated bisphenol A epoxy resin;

[0071] (2) Mix 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), stir at a speed of 400 rpm for 15 min, then add 25 g of dispersant BYK-2150 and 50 g of acetone, stir at a speed of 800 rpm for 15 min, then add 250 g of flake graphite (particle size D50 is 8.5 μm), stir at a speed of 1200 rpm for 45 min under a vacuum of -0.095 MPa, then add 12 g of fumed silica (specific surface area 380 m 2 / g) and 8 g of dioctyl phthalate, stir at 500 rpm for 30 min under a vacuum of -0.095 MPa to obtain 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 with bisphenol A epoxy resin;

[0074] The specific steps are as follows:

[0075] (1) Under a 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 3 times with petroleum ether, and vacuum dried to obtain a bis-epoxy quaternary ammonium salt;

[0076] (2) 28.5 g of the bis-epoxy quaternary ammonium salt was added to 170 g of deionized water, heated to 40 °C, stirred for 30 min, then 2.4 g of ethylenediamine and 0.8 g of tris(2-aminoethyl)amine were added, heated to 65 °C, reacted for 4 h, washed 3 times with absolute ethanol, and vacuum dried to obtain a branched quaternary ammonium salt containing epoxy groups;

[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, then 20 g of the branched quaternary ammonium salt containing epoxy groups was added, heated to 80 °C, stirred for 6 h, 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, stirred at a speed of 400 rpm for 15 min, then 25 g of dispersant BYK-2150 and 50 g of acetone were added, stirred at a speed of 800 rpm for 15 min, then 250 g of modified graphite was added, stirred at a speed of 1200 rpm for 45 min under a vacuum of -0.095 MPa, then 12 g of fumed silica (specific surface area 380 m 2 / g) and 8 g of dioctyl phthalate were added, and stirred at a speed of 500 rpm for 30 min under a vacuum of -0.095 MPa to obtain a conductive graphite paste.

[0079] Performance test:

[0080] Curing the sample: The conductive graphite paste prepared in the examples and comparative examples was injected into a mold and cured at a gradient temperature: the first stage was left standing at 50 °C for 2 h; the second stage was cured at 80 °C for 1 h; the third stage was cured at 120 °C for 0.5 h, and then naturally cooled to room temperature.

[0081] Volume resistivity: Detected according to GB / T 29417-2012, the volume resistivity was measured by the four-probe method. The specimen was cut into a size of 20 mm × 20 mm × 2 mm, and measured using a four-probe tester in an environment of 23 ± °C. The average value of three parallel tests was recorded, and the results are shown in Table 1.

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

[0083] Tensile strength at break: Tested according to GB / T 1040.1-2018. A tensile test was carried out using an electronic universal testing machine at a rate of 5 mm / min, 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 a cantilever beam impact tester, the notch depth of the specimen was 2 mm, the pendulum energy was 5.5 J, and 5 valid data were tested in each group. The average value was taken. The results are shown in Table 1.

[0085] Corrosion resistance test: Tested according to GB / T 1771-2007. A neutral salt spray test was carried out using a salt spray chamber. The specimen was placed at an angle of 45°, and a 5wt% NaCl solution was continuously sprayed. The temperature of the chamber was maintained at 35±2°C. After continuous testing for 240 h, it was taken out, rinsed with deionized water and dried, and then the volume resistivity change rate was measured. The average value of three parallel tests was taken for each group of data. The results are shown in Table 1.

[0086] Table 1 Performance test results

[0087]

[0088] Data analysis:

[0089] From the data of Examples 1-3 in Table 1, it can be seen that the conductive graphite adhesive prepared by the present invention exhibits excellent comprehensive performance in terms of volume resistivity, adhesion, tensile strength at break, impact strength, and corrosion resistance. This may be due to the introduction of a branched quaternary ammonium salt containing epoxy groups during the preparation process. Its special molecular structure can effectively improve the interfacial bonding force between graphite and matrix resin, thus significantly improving the conductivity and mechanical properties of the material. At the same time, the epoxy groups in the branched quaternary ammonium salt can undergo a cross-linking reaction with epoxy resin, further enhancing the structural stability and durability of the material. In addition, the branched structure of the branched quaternary ammonium salt may form a uniform dispersion layer on the graphite surface and an intercalation structure between layers, increasing the graphite layer spacing while avoiding the agglomeration of graphite particles, thereby improving the uniformity and stability of the conductive network. This molecular design and interfacial regulation strategy enable the conductive graphite adhesive of the present invention to exhibit excellent balance in various performance indicators and are suitable for application scenarios with high requirements for conductivity and mechanical properties.

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

[0091] From the data of Example 2 and Comparative Example 5 in Table 1, it can be seen that the sulfonated bisphenol A epoxy resin used in Example 2 has significant advantages in improving the performance of conductive graphite glue. The introduction of sulfonic acid groups may enhance the carrier mobility through the proton conduction mechanism, and its strong polar characteristics improve the interfacial wettability between the resin matrix and the filler. The sulfonated epoxy resin combined with modified graphite not only improves the stability of the conductive path, but also reduces the damage of the environmental medium to the conductive network through the charge shielding effect, significantly improving the performance retention rate of the material in the corrosive environment.

[0092] Those of ordinary skill in the art should understand that: the discussion of any above embodiment is only exemplary, and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A conductive graphite paste, 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 are mixed, cooled to 8-12°C, 3-5 g of N,N,N',N'-tetramethylethylenediamine is 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 tri(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 (particle size D50 is 8.5 μm) into 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 the 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 groups is 200-300:300-500:15-25.

2. The conductive graphite paste according to claim 1, characterized in that: 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, fuming sulfuric acid is added dropwise after stirring for 8-12 minutes, the dropping speed 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, the reaction is stirred for 3-5 hours, the temperature is lowered to room temperature after the reaction is completed, the mixture is poured into an ice-water mixture for quenching, sodium bicarbonate is added, the mixture is stirred for 20-40 minutes, the mixture is dialyzed for purification, and vacuum dried to obtain the sulfonated bisphenol A epoxy resin.

3. The conductive graphite paste according to claim 2, characterized in that: 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.

4. The conductive graphite paste according to claim 2, characterized in that: The SO3 content of the oleum is 20wt%-30wt%.

5. 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.

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

7. 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.

8. 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.

9. A method for preparing a conductive graphite paste according to any one of claims 1 to 8, 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 300-500rpm for 10-20min, dispersant and acetone are added, stirred at a speed of 700-900rpm for 10-20min, modified graphite is added, stirred at a speed of 1000-1500rpm for 40-50min at a vacuum degree of -0.095±0.002MPa, fumed silica and plasticizer are added, stirred at a speed of 400-600rpm for 25-35min at a vacuum degree of -0.095±0.002MPa, to obtain conductive graphite glue.

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