A pure silver epoxy conductive adhesive composition, a pure silver epoxy conductive adhesive, and a preparation method and application thereof

Abstract

The present application relates to the technical field of conductive adhesives, and specifically discloses a pure silver epoxy conductive adhesive composition, a pure silver epoxy conductive adhesive, and a preparation method and application thereof. The present application discloses a pure silver epoxy conductive adhesive composition, comprising the following components in parts by weight: 26-34 parts of castor oil modified silver powder; 8-12 parts of epoxy resin; 0.7-1.3 parts of curing agent; 8-15 parts of active diluent; 2-5 parts of coupling agent; 7-12 parts of toughening agent; 3-8 parts of synergist; the synergist includes isocyanate and organic acid zinc. The present application also discloses a pure silver epoxy conductive adhesive prepared from the above composition, a preparation method and application thereof. The pure silver epoxy conductive adhesive prepared in the present application has high conductivity and shear strength, and can be cured under different temperature conditions, with a short curing time, which can meet the production process and application requirements of electronic products for different packaging temperatures.

Description

Technical Field

[0001] The present application relates to the technical field of conductive adhesives, and particularly relates to a pure silver epoxy conductive adhesive composition, a pure silver epoxy conductive adhesive, and a preparation method and application thereof. Background Art

[0002] With the vigorous development of electronic technology, electronic products tend to develop in the directions of miniaturization, portability, and high integration. The traditional method of conductive connection in electronic products is often welding. However, this process method is prone to problems such as deformation of electronic components, loose joints, and performance degradation, and cannot meet the requirements of the process and applications. Currently, the conductive adhesive bonding method to replace the welding process has emerged. The conductive adhesive can avoid the adverse effects of welding and is an ideal choice for achieving conductive connection in electronic products.

[0003] As an adhesive that has conductivity after curing or drying, the conductive adhesive usually uses the bonding effect of the matrix resin to bind conductive particles together to form a conductive path, thereby achieving the conductive connection of the adhered materials. If the ratio of the matrix resin and the conductive particles is changed, the performance of the conductive adhesive can be changed. In order to develop a conductive adhesive with high conductivity, it is necessary to increase the proportion of conductive particles. However, as the addition amount of the conductive particles increases, it becomes difficult for the conductive particles to be uniformly dispersed in the resin, and the shear strength of the prepared conductive adhesive decreases.

[0004] In addition, with the development of technology, different types of electronic products have different requirements for the encapsulation temperature, which requires the conductive adhesive to be able to cure under different temperature conditions in order to meet the existing production process and application requirements. However, the conductive adhesives on the market currently can only cure at a specific temperature and have a long curing time, thus limiting the application of the conductive adhesive. Summary of the Invention

[0005] In order to provide a conductive adhesive that can be cured under different temperature conditions and at the same time improve the conductivity and shear strength of the conductive adhesive, the present application provides a pure silver epoxy conductive adhesive composition, a pure silver epoxy conductive adhesive, and a preparation method and application thereof.

[0006] In the first aspect, the present application provides a pure silver epoxy conductive adhesive composition, adopting the following technical solution:

[0007] A pure silver epoxy conductive adhesive composition, comprising the following components in parts by weight:

[0008] Castor oil-modified silver powder 26 - 34 parts; epoxy resin 8 - 12 parts; curing agent 0.7 - 1.3 parts; active diluent 8 - 15 parts; coupling agent 2 - 5 parts; toughening agent 7 - 12 parts; synergist 3 - 8 parts; the synergist includes isocyanate and zinc organic acid.

[0009] By adopting the above technical solutions, the present application uses isocyanate and zinc organic acid as synergists, which cooperate synergistically with castor oil-modified silver powder, epoxy resin, curing agent, active diluent, coupling agent, and toughening agent, to obtain a pure silver epoxy conductive adhesive that can be cured under different temperature conditions and has a short curing time. At the same time, the cured pure silver epoxy conductive adhesive has high conductivity and shear strength, indicating that the pure silver epoxy conductive adhesive prepared by the present application has excellent performance.

[0010] Castor oil is a triglyceride of fatty acids, with abundant hydroxyl groups, double bonds, and ester bonds. After the present application uses castor oil to modify silver powder, it can effectively improve the uniform dispersion of silver powder. And during the preparation of the pure silver epoxy conductive adhesive, the castor oil-modified silver powder containing abundant functional groups is beneficial to form a strong network structure in the conductive adhesive system, which is beneficial to expanding the volatilization path of the solvent in the pure silver epoxy conductive adhesive and promoting the rapid curing of the conductive adhesive. At the same time, using the above technical solutions effectively reduces the sedimentation of silver powder in the pure silver epoxy conductive adhesive, improves the conductivity and shear strength of the conductive adhesive, and makes the overall performance of the conductive adhesive more uniform and stable.

[0011] At the same time, through experimental analysis, the present application finds that compared with using pure silver powder, after using castor oil to modify silver powder for preparing the pure silver epoxy conductive adhesive, on the premise of maintaining excellent electrical conductivity, it can significantly improve the curing effect and shear strength of the pure silver epoxy conductive adhesive.

[0012] Preferably, the castor oil-modified silver powder is prepared from castor oil and silver powder with a weight ratio of (0.3 - 0.5):30.

[0013] In a specific embodiment, the weight ratio of the castor oil to the silver powder can be: 0.3:30, 0.4:30, 0.5:30.

[0014] In some specific embodiments, the weight ratio of the castor oil to the silver powder can also be: (0.3 - 0.4):30, (0.4 - 0.5):30.

[0015] Through experimental analysis, it is found that when the weight ratio of castor oil to silver powder is controlled within the above range, the curing effect, conductivity, and shear strength of the pure silver epoxy conductive adhesive can be further improved. Therefore, the present application controls the weight ratio of castor oil to silver powder within the above range.

[0016] Preferably, the particle size of the silver powder is 80 - 200 nm.

[0017] When the particle size of the silver powder is too small, the specific surface area is relatively large, and the silver powder is prone to agglomeration, resulting in poor modification effect of the castor oil-modified silver powder and uneven dispersion in the conductive adhesive; while when the particle size of the silver powder is too large, the conductivity of the silver powder is poor, leading to a decrease in the conductivity of the prepared pure silver epoxy conductive adhesive. Therefore, the particle size of the silver powder in this application is controlled within the above range.

[0018] The isocyanate structure contains unsaturated bonds and thus has high reactivity. It is found in this application that when an appropriate amount of isocyanate is used in combination with zinc organic acid as a synergist for preparing the pure silver epoxy conductive adhesive, it can promote the initiation, growth, and crosslinking of free radicals in the pure silver epoxy conductive adhesive system, making the components in the pure silver epoxy conductive adhesive in a relatively balanced state, which is beneficial to improving the overall compactness of the pure silver epoxy conductive adhesive, thereby enhancing the conductivity and shear strength of the pure silver epoxy conductive adhesive. On the other hand, the isocyanate can react with the epoxy resin with active hydrogen, which is conducive to increasing the binding ability between the components inside the pure silver epoxy conductive adhesive and helps to achieve rapid curing.

[0019] Through experimental analysis in this application, it can be seen that compared with not using a synergist or only using one of isocyanate and zinc organic acid as a synergist, choosing to use isocyanate and zinc organic acid simultaneously as a synergist in this application can further improve the curing effect, conductivity, and shear strength of the pure silver epoxy conductive adhesive.

[0020] Preferably, the weight ratio of the isocyanate to the zinc organic acid is 5.5:(1 - 3).

[0021] In a specific embodiment, the weight ratio of the isocyanate to the zinc organic acid can be: 5.5:1, 5.5:2, 5.5:3.

[0022] In some specific embodiments, the weight ratio of the isocyanate to the zinc organic acid can also be: 5.5:(1 - 2), 5.5:(2 - 3).

[0023] Through experimental analysis, it can be seen that when the weight ratio of isocyanate and zinc organic acid in the synergist is controlled within the above range, the curing effect, conductivity, and shear strength of the pure silver epoxy conductive adhesive can be further improved. Therefore, the weight ratio of isocyanate and zinc organic acid in this application is controlled within the above range.

[0024] Further, the zinc organic acid is selected from at least one of zinc gluconate, zinc methionine, and zinc lactate.

[0025] Further, the isocyanate is selected from at least one of xylylene diisocyanate, toluene diisocyanate dimer, triphenylmethane triisocyanate, toluene diisocyanate, and cyclohexane dimethylene diisocyanate.

[0026] Preferably, the curing agent is selected from at least one of aliphatic polyamines, cycloaliphatic polyamines, and low molecular weight polyamides.

[0027] Further, the aliphatic polyamine is selected from at least one of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine.

[0028] Epoxy resins can be cured at room temperature or below 150 °C. They need to react with a curing agent to form a three-dimensional structure to have practical value. The structure and quality of the curing agent will directly affect the application effect of the epoxy resin. In this application, at least one of aliphatic polyamines, cycloaliphatic polyamines, and low molecular weight polyamides with relatively high activity is selected as the curing agent, which is beneficial to realizing the crosslinking and curing of epoxy resins with other components.

[0029] Preferably, the active diluent is selected from at least one of neopentyl glycol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, 2-ethylhexyl glycidyl ether, butyl glycidyl ether, o-cresol glycidyl ether, phenyl glycidyl ether, 1,4-butanediol diglycidyl ether, p-methylphenyl glycidyl ether, polypropylene glycol diglycidyl ether, and p-tert-butylphenyl glycidyl ether.

[0030] Preferably, the coupling agent is at least one of silane coupling agents and titanate coupling agents.

[0031] Preferably, the toughening agent is at least one of carboxyl-terminated nitrile rubber, hydroxyl-terminated nitrile rubber, and epoxy-terminated nitrile rubber.

[0032] In a second aspect, this application provides a pure silver epoxy conductive adhesive, which is prepared from the above-mentioned pure silver epoxy conductive adhesive composition.

[0033] In a third aspect, this application provides a preparation method for the above-mentioned pure silver epoxy conductive adhesive, which specifically includes the following steps:

[0034] S1: The silver powder is fully dispersed in an alcohol solvent, and the castor oil is added. After ultrasonic oscillation reaction and drying, the castor oil-modified silver powder is obtained.

[0035] S2: According to the formula, the epoxy resin, the curing agent, the active diluent, the coupling agent, the toughening agent, and the synergist are fully mixed to prepare a mixture.

[0036] S3: The castor oil-modified silver powder is added to the mixture prepared in step S2, and stirred and mixed fully to obtain the pure silver epoxy conductive adhesive.

[0037] Preferably, the alcohol solvent is selected from at least one of ethanol, methanol, and isopropanol.

[0038] Preferably, the parameter conditions of the ultrasonic oscillation reaction are as follows: ultrasonic frequency 20 - 28 kHz; temperature 40 - 50 °C; time 30 - 60 min.

[0039] Fourthly, the present application also provides the application of the above pure silver epoxy conductive adhesive in conductive materials.

[0040] The pure silver epoxy conductive adhesive provided by the present application has high conductivity and shear strength; and can be cured under different temperature conditions with a short curing time, thus meeting the production process and application requirements of electronic products for different packaging temperatures and broadening the application of pure silver epoxy conductive adhesives in conductive materials.

[0041] In summary, the technical solution of the present application has the following effects:

[0042] The present application uses isocyanate and zinc organic acid as synergists, and cooperates synergistically with castor oil-modified silver powder, epoxy resin, curing agent, active diluent, coupling agent, and toughening agent to obtain a pure silver epoxy conductive adhesive with high conductivity and shear strength. At the same time, the pure silver epoxy conductive adhesive prepared by the present application can be cured under different temperature conditions and has a short curing time, thus meeting the production process and application requirements of electronic products for different packaging temperatures.

[0043] The present application further improves the curing effect, conductivity, and shear strength of the pure silver epoxy conductive adhesive by screening the dosages of each component in the pure silver epoxy conductive adhesive, and simultaneously screening the weight ratio of castor oil to silver powder and the weight ratio of isocyanate to zinc organic acid. Specific Embodiments

[0044] Firstly, the present application provides a pure silver epoxy conductive adhesive, which comprises the following components in parts by weight: 26 - 34 parts of castor oil-modified silver powder; 8 - 12 parts of epoxy resin; 0.7 - 1.3 parts of curing agent; 8 - 15 parts of active diluent; 2 - 5 parts of coupling agent; 7 - 12 parts of toughening agent; 3 - 8 parts of synergist; wherein, the synergist includes isocyanate and zinc organic acid.

[0045] Specifically, the castor oil-modified silver powder is prepared from castor oil and silver powder with a particle size of 80 - 200 nm at a weight ratio of (0.3 - 0.5):30.

[0046] At the same time, the weight ratio of isocyanate to zinc organic acid is 5.5:(1 - 3).

[0047] Furthermore, the zinc organic acid is selected from at least one of zinc gluconate, zinc methionine, and zinc lactate.

[0048] Furthermore, the isocyanate is selected from at least one of xylylene diisocyanate, toluene diisocyanate dimer, triphenylmethane triisocyanate, toluene diisocyanate, and cyclohexane dimethylene diisocyanate.

[0049] The curing agent is selected from at least one of aliphatic polyamines, alicyclic polyamines and low molecular weight polyamides.

[0050] Furthermore, the aliphatic polyamine is at least one selected from ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine.

[0051] Among them, the active diluent is selected from at least one of neopentyl glycol glycidyl ether, cyclohexyl dimethanol diglycidyl ether, 2-ethylhexyl glycidyl ether, butyl glycidyl ether, o-cresol glycidyl ether, phenyl glycidyl ether, 1,4-butanediol diglycidyl ether, p-methylphenyl glycidyl ether, polypropylene glycol diglycidyl ether, and p-tert-butylphenyl glycidyl ether.

[0052] Furthermore, the coupling agent is selected from at least one of a silane coupling agent and a titanate coupling agent.

[0053] Furthermore, the toughening agent is selected from at least one of carboxyl-terminated nitrile rubber, hydroxyl-terminated nitrile rubber, and epoxy-terminated nitrile rubber.

[0054] In a second aspect, the present application provides a pure silver epoxy conductive adhesive prepared using the above-mentioned pure silver epoxy conductive adhesive composition.

[0055] In a third aspect, the present application provides a method for preparing the above-mentioned pure silver epoxy conductive adhesive, which specifically comprises the following steps:

[0056] S1: Fully disperse the silver powder in an alcohol solvent, add castor oil, and obtain castor oil-modified silver powder through ultrasonic oscillation reaction and drying. The ultrasonic oscillation parameters are as follows: ultrasonic frequency 20-28kHz; temperature 40-50°C; time 30-60min.

[0057] S2: According to the formula, the epoxy resin, the curing agent, the reactive diluent, the coupling agent, the toughening agent and the synergist are fully mixed to prepare a mixture;

[0058] S3: adding the castor oil-modified silver powder to the mixture prepared in step S2, stirring and mixing thoroughly to obtain a pure silver epoxy conductive adhesive.

[0059] In a fourth aspect, the present application provides the application of the above-mentioned pure silver epoxy conductive adhesive in conductive materials.

[0060] Unless otherwise specified, the reagents, methods and equipment used in this application are conventional reagents, methods and equipment in this technical field.

[0061] The present application is further described in detail below in conjunction with Examples 1-13, Comparative Examples 1-8 and performance testing experiments. These examples should not be construed as limiting the scope of protection claimed in the present application.

[0062] Example

[0063] Examples 1-7

[0064] Examples 1-7 respectively provide a pure silver epoxy conductive adhesive.

[0065] The differences among the above embodiments are: the amount of castor oil modified silver powder added and the weight ratio of castor oil to silver powder, as shown in Table 1.

[0066] The implementation method of the above embodiment specifically includes the following steps:

[0067] S1: Add 30 g of silver powder with a particle size of 150 nm into 200 mL of ethanol, perform ultrasonic vibration to fully disperse the silver powder, then add castor oil, and react for 40 minutes at an ultrasonic frequency of 25 kHz and a temperature of 45°C. After the reaction, dry the mixture at 80°C to obtain castor oil-modified silver powder.

[0068] S2: According to the formula, 10 g of BPA-PA phenolic epoxy resin, 1 g of diethylenetriamine as a curing agent, 10 g of neopentyl glycol glycidyl ether as a reactive diluent, 3.5 g of KH560 as a coupling agent, 9.8 g of carboxyl-terminated nitrile rubber as a toughening agent and 5 g of a synergist were weighed and mixed thoroughly to prepare a mixture; wherein, 5 g of the synergist consisted of xylene diisocyanate and zinc gluconate in a weight ratio of 5.5:2.

[0069] S3: Add the castor oil modified silver powder to the mixture prepared in step S2, stir and mix thoroughly, and under vacuum, N 2 The package is sealed to obtain the pure silver epoxy conductive adhesive.

[0070] Table 1 Addition amount of castor oil modified silver powder and weight ratio of castor oil to silver powder in Examples 1-7

[0071]

[0072] Embodiment 8-13

[0073] Examples 8-13 respectively provide a pure silver epoxy conductive adhesive.

[0074] The difference between the above embodiments and embodiment 2 is the weight ratio of isocyanate to organic acid zinc, as shown in Table 2.

[0075] Table 2 Weight ratio of isocyanate and organic acid zinc in Examples 2, 8-13

[0076]

[0077]

[0078] Comparative Example

[0079] Comparative Example 1

[0080] This comparative example provides a pure silver epoxy conductive adhesive.

[0081] The difference between this comparative example and Example 2 is that:

[0082] The preparation method of pure silver epoxy conductive adhesive in this comparative example is:

[0083] S1: According to the formula, 10 g of BPA-PA phenolic epoxy resin, 1 g of diethylenetriamine as a curing agent, 10 g of neopentyl glycol glycidyl ether as a reactive diluent, 3.5 g of KH560 as a coupling agent, 9.8 g of carboxyl-terminated nitrile rubber as a toughening agent and 5 g of a synergist were weighed and fully mixed to prepare a mixture; wherein the 5 g of the synergist consisted of xylene diisocyanate and zinc gluconate in a weight ratio of 5.5:2.

[0084] S2: Weigh 30 g of silver powder with a particle size of 150 nm, add it to the mixture prepared in step S2, stir and mix thoroughly, and under vacuum, 2 The package is sealed to obtain the pure silver epoxy conductive adhesive.

[0085] Comparative Example 2

[0086] This comparative example provides a pure silver epoxy conductive adhesive.

[0087] The difference between this comparative example and Example 2 is that the added amount of castor oil modified silver powder is 24 g.

[0088] Comparative Example 3

[0089] This comparative example provides a pure silver epoxy conductive adhesive.

[0090] The difference between this comparative example and Example 2 is that the added amount of castor oil modified silver powder is 36 g.

[0091] Comparative Example 4

[0092] This comparative example provides a pure silver epoxy conductive adhesive.

[0093] The difference between this comparative example and Example 2 is that:

[0094] The preparation method of pure silver epoxy conductive adhesive in this comparative example is:

[0095] S1: Add 30 g of silver powder with a particle size of 150 nm into 200 mL of ethanol, perform ultrasonic vibration to fully disperse the silver powder, then add castor oil, and react for 40 minutes at an ultrasonic frequency of 25 kHz and a temperature of 45°C. After the reaction, dry the mixture at 80°C to obtain castor oil-modified silver powder.

[0096] S2: According to the formula, 10 g of BPA-PA phenolic epoxy resin, 1 g of diethylenetriamine as a curing agent, 10 g of neopentyl glycol glycidyl ether as a reactive diluent, 3.5 g of KH560 as a coupling agent, and 9.8 g of carboxyl-terminated nitrile rubber as a toughening agent were weighed to prepare a mixture.

[0097] S3: Add the castor oil modified silver powder to the mixture prepared in step S2, stir and mix thoroughly, and under vacuum, N 2 The package is sealed to obtain the pure silver epoxy conductive adhesive.

[0098] Comparative Example 5

[0099] This comparative example provides a pure silver epoxy conductive adhesive.

[0100] The difference between this comparative example and Example 2 is that:

[0101] The preparation method of pure silver epoxy conductive adhesive in this comparative example is:

[0102] S1: Add 30 g of silver powder with a particle size of 150 nm into 200 mL of ethanol, perform ultrasonic vibration to fully disperse the silver powder, then add castor oil, and react for 40 minutes at an ultrasonic frequency of 25 kHz and a temperature of 45°C. After the reaction, dry the mixture at 80°C to obtain castor oil-modified silver powder.

[0103] S2: According to the formula, 10 g of BPA-PA phenolic epoxy resin, 1 g of diethylenetriamine as a curing agent, 10 g of neopentyl glycol glycidyl ether as a reactive diluent, 3.5 g of KH560 as a coupling agent, 9.8 g of carboxyl-terminated nitrile rubber as a toughening agent and 5 g of xylene diisocyanate as an isocyanate were weighed and mixed thoroughly to prepare a mixture.

[0104] S3: Add the castor oil modified silver powder to the mixture prepared in step S2, stir and mix thoroughly, and under vacuum, N 2 The package is sealed to obtain the pure silver epoxy conductive adhesive.

[0105] Comparative Example 6

[0106] This comparative example provides a pure silver epoxy conductive adhesive.

[0107] The difference between this comparative example and Example 2 is as follows:

[0108] In this comparative example, the preparation method of the pure silver epoxy conductive adhesive is as follows:

[0109] S1: Add 30 g of silver powder with a particle size of 150 nm to 200 mL of ethanol, ultrasonically oscillate to fully disperse the silver powder, then add castor oil, and react at a condition of an ultrasonic frequency of 25 kHz and a temperature of 45 °C for 40 min. After the reaction, dry it at 80 °C to obtain castor oil-modified silver powder;

[0110] S2: According to the formula, weigh 10 g of BPA-PA phenolic epoxy resin, 1 g of diethylenetriamine as a curing agent, 10 g of neopentyl glycol diglycidyl ether as an active diluent, 3.5 g of KH560 as a coupling agent, 9.8 g of carboxyl-terminated nitrile rubber as a toughening agent, and 5 g of zinc gluconate as an organic acid zinc, and fully mix them to obtain a mixture.

[0111] S3: Add the castor oil-modified silver powder to the mixture prepared in step S2, fully stir and mix, and under vacuum conditions, N 2 Seal and package to obtain the pure silver epoxy conductive adhesive.

[0112] Comparative Example 7

[0113] This comparative example provides a pure silver epoxy conductive adhesive.

[0114] The difference between this comparative example and Example 2 is that the addition amount of the synergist is 2 g.

[0115] Comparative Example 8

[0116] This comparative example provides a pure silver epoxy conductive adhesive.

[0117] The difference between this comparative example and Example 2 is that the addition amount of the synergist is 9 g.

[0118] Performance detection test

[0119] Taking the pure silver epoxy conductive adhesives in Examples 1-13 and Comparative Examples 1-8 as the detection objects, detect the curing time, volume resistivity, and shear strength of the pure silver epoxy conductive adhesives.

[0120] The technical index requirements for the pure silver epoxy conductive adhesive are: volume resistivity ≤ 0.0004 Ω·cm, thermal conductivity higher than 2.5 W / m·k, glass transition temperature Tg greater than 80 °C, viscosity (23 °C, 100 rpm) of 2200 - 3200 cPs, and tensile shear strength higher than 1475 psi.

[0121] (1) Curing time: The pure silver epoxy conductive adhesives in Examples 1-13 and Comparative Examples 1-8 were coated on the glass surface with a coating area of a dot with a diameter of 1 mm, and were respectively placed under different temperatures (80 °C, 100 °C, 120 °C, 150 °C, 175 °C). When the resistance remained constant, the curing was complete, and the curing time of the pure silver epoxy conductive adhesive was recorded. Note: When the curing time ≤ 1 min, the curing effect was observed every 5 s; when 1 min < curing time ≤ 10 min, the curing effect was observed every 0.5 min; when 10 min < curing time ≤ 60 min, the curing effect was observed every 1 min; when 60 min < curing time ≤ 240 min, the curing effect was observed every 5 min.

[0122] (2) Volume resistivity: The volume resistivity of the pure silver epoxy conductive adhesive was detected according to the test standard method of ASTM D257.

[0123] (3) Thermal conductivity: The thermal conductivity of the pure silver epoxy conductive adhesive was detected according to the test standard method of ASTM E1461-07.

[0124] (4) Glass transition temperature: The glass transition temperature of the pure silver epoxy conductive adhesive was detected according to the test standard method of GB / T 19466.2-2004.

[0125] (5) Viscosity (23 °C, 100 rpm): The glass transition temperature of the pure silver epoxy conductive adhesive was detected according to the test standard method of GB / T 2794-2013.

[0126] (6) Tensile shear strength: The tensile shear strength of the pure silver epoxy conductive adhesive was detected according to the test standard method of GB / T 7124-2008. Test results: As shown in Table 3.

[0127] Table 3 Performance test results of the pure silver epoxy conductive adhesives in Examples 1-13 and Comparative Examples 1-8

[0128]

[0129]

[0130] Combined with Table 3, by comparing the test results of Examples 1-13 and Comparative Examples 1-8, the present application uses isocyanate and zinc organic acid as synergists, and cooperates synergistically with castor oil-modified silver powder, epoxy resin, curing agent, active diluent, coupling agent, and toughening agent to prepare the pure silver epoxy conductive adhesive. The curing conditions are as follows: the curing time is ≤185 min at 80 °C, ≤140 min at 100 °C, ≤20 min at 120 °C, ≤8.5 min at 150 °C, ≤1 min at 175 °C, the volume resistivity is lower than ≤0.0004 Ω·cm, the thermal conductivity is higher than 2.5 W / m·k, the glass transition temperature Tg is greater than 80 °C, the viscosity (23 °C, 100 rpm) is 2200-3200 cPs, and the tensile shear strength is higher than 1475 psi. The above test results show that the curing effect of the pure silver epoxy conductive adhesive prepared by using the formula and test method provided by the present application is good; and the comprehensive performance of the pure silver epoxy conductive adhesive is relatively excellent, specifically manifested in: lower volume resistivity, higher thermal conductivity, higher glass transition temperature, viscosity meeting the actual application requirements, and higher tensile shear strength.

[0131] By comparing the test results of Example 2 and Comparative Example 1, compared with using pure silver powder, after the silver powder is modified with castor oil in the present application and used to prepare the pure silver epoxy conductive adhesive, on the premise of maintaining excellent electrical conductivity, the curing effect and shear strength of the pure silver epoxy conductive adhesive can be significantly improved. Therefore, the present application uses castor oil-modified silver powder to prepare the pure silver epoxy conductive adhesive.

[0132] By comparing the test results of Examples 1-3 and Comparative Examples 2-3, when the addition amount of castor oil-modified silver powder is less than 26 parts, the curing effect and shear strength performance of the pure silver epoxy conductive adhesive are not significantly improved, but the electrical conductivity significantly decreases; when the addition amount of castor oil-modified silver powder is greater than 34 parts, the electrical conductivity of the pure silver epoxy conductive adhesive is not significantly improved, but the curing effect and shear strength performance of the pure silver epoxy conductive adhesive are poor. Therefore, the present application controls the addition amount of castor oil-modified silver powder in the range of 26-34 parts.

[0133] By comparing the test results of Examples 2, 4-7, when the weight ratio of castor oil to silver powder is controlled in the range of (0.3-0.5):30, the curing effect, electrical conductivity and shear strength of the pure silver epoxy conductive adhesive can be further improved. Therefore, the present application controls the weight ratio of castor oil to silver powder in the above range.

[0134] By comparing the test results of Example 2 with those of Comparative Examples 4-6, compared with not using a synergist or only using one of isocyanate and zinc organic acid as a synergist, the present application selects to use isocyanate and zinc organic acid simultaneously as a synergist, which can further improve the curing effect, conductivity and shear strength of the pure silver epoxy conductive adhesive. Therefore, the present application selects to use isocyanate and zinc organic acid simultaneously as a synergist.

[0135] By comparing the test results of Example 2, Examples 8-9 with those of Comparative Examples 7-8, when the addition amount of the synergist is less than 3 parts, the conductivity of the pure silver epoxy conductive adhesive is not significantly improved, but the curing effect and shear strength performance of the pure silver epoxy conductive adhesive are poor; when the addition amount of the synergist is greater than 8 parts, the curing effect and shear strength performance of the pure silver epoxy conductive adhesive are not significantly improved, but the conductivity decreases significantly. Therefore, the present application controls the addition amount of the synergist within the range of 3-8 parts.

[0136] By comparing the test results of Example 2, Examples 10-13, when the weight ratio of isocyanate and zinc organic acid in the synergist is controlled within the range of 5.5:(1-3), the curing effect, conductivity and shear strength of the pure silver epoxy conductive adhesive can be further improved. Therefore, the present application controls the weight ratio of isocyanate and zinc organic acid within the above range.

[0137] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A pure silver epoxy conductive adhesive composition, characterized in that, it comprises the following components in parts by weight: 26 - 34 parts of castor oil modified silver powder; 8 - 12 parts of epoxy resin; 0.7 - 1.3 parts of curing agent; 8 - 15 parts of active diluent; 2 - 5 parts of coupling agent; 7 - 12 parts of toughening agent; 3 - 8 parts of synergist; the synergist comprises isocyanate and zinc gluconate; the weight ratio of the isocyanate to the zinc gluconate is 5.5:(1 - 3).

2. The pure silver epoxy conductive adhesive composition according to claim 1, characterized in that, the castor oil modified silver powder is prepared from castor oil and silver powder with a weight ratio of (0.3 - 0.5):

30.

3. The pure silver epoxy conductive adhesive composition according to claim 1, characterized in that, the particle size of the silver powder is 80 - 200 nm.

4. The pure silver epoxy conductive adhesive composition according to claim 1, characterized in that, the isocyanate is selected from at least one of benzylidene diisocyanate, toluene diisocyanate dimer, triphenylmethane triisocyanate, toluene diisocyanate, cyclohexane dimethylene diisocyanate.

5. A pure silver epoxy conductive adhesive, characterized in that, the pure silver epoxy conductive adhesive is prepared from the pure silver epoxy conductive adhesive composition according to any one of claims 1 - 4.

6. The preparation method of the pure silver epoxy conductive adhesive according to claim 5, characterized in that, it specifically comprises the following steps: S1: Fully disperse the silver powder in an alcohol solvent, add the castor oil, and obtain the castor oil modified silver powder through ultrasonic oscillation reaction and drying; S2: According to the formula, fully mix the epoxy resin, the curing agent, the active diluent, the coupling agent, the toughening agent and the synergist to prepare a mixture; S3: Add the castor oil modified silver powder to the mixture prepared in step S2, and fully stir and mix to obtain the pure silver epoxy conductive adhesive.

7. The preparation method of the pure silver epoxy conductive adhesive according to claim 6, characterized in that, the parameter conditions of the ultrasonic oscillation reaction are: ultrasonic frequency 20 - 28 kHz; temperature 40 - 50 °C; time 30 - 60 min.

8. The application of the pure silver epoxy conductive adhesive according to claim 5 in conductive materials.

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