Modified epoxy resin conductive adhesive and preparation method thereof

Abstract

The invention relates to the technical field of conductive adhesives, and discloses a modified epoxy resin conductive adhesive and a preparation method thereof.The modified epoxy resin conductive adhesive is prepared from, by weight, 25-35 parts of epoxy resin, 1.05-2.1 parts of diphenyl carbonate, 0.24-0.48 part of formaldehyde, 1-2 parts of conductive filler, 0.005-0.01 part of a catalyst, 1.25-2.5 parts of a flame retardant, 0.2-0.4 part of a plasticizer, 0.1-0.3 part of a curing agent and 0.1-0.3 part of N, N-dimethylformamide. 15 parts of an N, N-dimethylformamide solvent and 75 parts of an acetonitrile solvent; dihydroxy carbazole is used as a conductive filler, a brominated reaction flame retardant is used as a flame retardant, the conductive filler and the flame retardant are combined through formaldehyde to prepare a polycarbonate modified intermediate with diphenyl carbonate through a transesterification melt polycondensation method, and then the polycarbonate modified intermediate is uniformly mixed and stirred with epoxy resin, a plasticizer and a curing agent to obtain the modified epoxy resin conductive adhesive. The modified epoxy resin conductive adhesive prepared by the invention has relatively good conductivity, flame retardance and heat resistance.

Description

Technical Field

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

[0002] With the rapid development of electronic information technology, traditional lead-tin solder is no longer suitable for electronic packaging technology, so the development and application of conductive adhesives have attracted extensive attention. Conductive adhesives are essentially an adhesive, which is different from ordinary adhesives in that conductive fillers are added to the matrix to give it conductive properties.

[0003] Epoxy resin conductive adhesive is composed of epoxy resin matrix, conductive filler, etc. The epoxy resin matrix has good bonding performance, but its flame retardant and heat resistance are poor. Conductive fillers are mainly divided into three categories: metal, carbon series, and composite. Metals mostly use Cu, Ni, Zn, etc., but these metals are easily oxidized after high-temperature sintering in the conductive adhesive, affecting conductivity and heat resistance. Common carbon series include graphene, which is a two-dimensional carbon-based structural material with relatively excellent electrical conductivity, thermal conductivity and other properties. Patent CN103614098B discloses a functionalized graphene-doped epoxy resin conductive adhesive and a preparation method thereof. The invention uses epoxy resin, graphene, silver nanowires, etc. as raw materials, and the prepared conductive adhesive has good conductivity and bonding strength, and has broad application prospects, but does not improve the heat resistance and poor flame retardancy of epoxy resin conductive adhesive. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the present invention aims to provide a modified epoxy resin conductive adhesive and a preparation method thereof, wherein the prepared conductive adhesive has excellent conductivity, heat resistance and flame retardancy.

[0005] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0006] A modified epoxy resin conductive adhesive comprises, by weight, 25-35 parts of epoxy resin, 1.05-2.1 parts of diphenyl carbonate, 0.24-0.48 parts of formaldehyde, 1-2 parts of conductive filler, 0.005-0.01 parts of catalyst, 1.25-2.5 parts of flame retardant, 0.2-0.4 parts of plasticizer, 0.1-0.3 parts of curing agent, 15 parts of N,N-dimethylformamide solvent and 75 parts of acetonitrile solvent.

[0007] Preferably, the conductive filler is 2,7-dihydroxycarbazole.

[0008] Preferably, the catalyst is lithium acetylacetonate.

[0009] Preferably, the flame retardant is a bromine-based reactive flame retardant.

[0010] Preferably, the bromine-based reactive flame retardant is one of 2,6-dibromophenol, 3,5-dibromophenol and 2,4,6-tribromophenol.

[0011] Preferably, the plasticizer is one of dibutyl isophthalate, dioctyl isophthalate, dibutyl terephthalate, dioctyl terephthalate, diethylene glycol benzoate, and propylene glycol sebacate.

[0012] Preferably, the curing agent is one of diaminocyclohexane, methylenebiscyclohexaneamine and diethylenetriamine.

[0013] The method for preparing the modified epoxy resin conductive adhesive comprises the following steps:

[0014] (1) Adding a conductive filler, a flame retardant, and formaldehyde to an N,N-dimethylformamide solvent, stirring and dispersing, heating to 60-80° C., and reacting for 5-10 hours. After the reaction is completed, adding water to precipitate the product, filtering, washing with methanol, and drying to obtain an intermediate 1;

[0015] (2) subjecting the intermediate 1, diphenyl carbonate and the catalyst to an ester exchange reaction at normal pressure and 160-250° C. for 2-4 hours under nitrogen protection, then reducing the pressure to 0.1-0.5 Torr and heating to 250-300° C. for polycondensation reaction for 1-2 hours. After the reaction is completed, heating is stopped, nitrogen is introduced to restore the system to normal pressure and the system is cooled to room temperature to obtain a polycarbonate modified intermediate 2;

[0016] (3) Add epoxy resin to acetonitrile solvent, stir and disperse, then add polycarbonate modified intermediate 2, plasticizer, and curing agent, stir well, apply the mixture evenly on a glass sheet, place in an oven at 120° C. for curing for 2 h, and obtain a modified epoxy resin conductive adhesive.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention uses 2,7-dihydroxycarbazole as a conductive filler. Carbazole is a type of hole transport material, which has a large conjugated system in its structure, which is conducive to the migration of electrons, and is therefore widely used in the field of photoconductive materials. 2,7-dihydroxycarbazole is combined with a bromine-based reactive flame retardant via formaldehyde, and then esterified with diphenyl carbonate and polycondensed to prepare a polycarbonate-based modified intermediate. The large π bond and p-π conjugated system in its main chain can well improve the conductivity of the conductive adhesive, while the bromine-based reactive flame retardant on the side chain improves the flame retardancy of the conductive adhesive. A modified epoxy resin conductive adhesive prepared by the present invention contains a large number of rigid structures, such as benzene rings, carbazole, and polycarbonate. The introduction of these rigid structures increases the molecular packing density of the material, thereby improving the heat resistance of the epoxy resin conductive adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a preparation route for the polycarbonate modified intermediate 2 of the present invention. DETAILED DESCRIPTION

[0020] The modified epoxy resin conductive adhesive and its preparation method of the present invention are further described below in conjunction with the embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention.

[0021] Embodiment 1:

[0022] A modified epoxy resin conductive adhesive comprises, by weight, 25 parts of epoxy resin, 1.05 parts of diphenyl carbonate, 0.24 parts of formaldehyde, 1 part of 2,7-dihydroxycarbazole, 0.005 parts of lithium acetylacetonate, 1.25 parts of 2,6-dibromophenol, 0.2 parts of dibutyl terephthalate, 0.1 parts of diaminocyclohexane, 15 parts of N,N-dimethylformamide solvent and 75 parts of acetonitrile solvent.

[0023] The preparation method of the modified epoxy resin conductive adhesive described in this embodiment is as follows:

[0024] (1) Add 1 part of 2,7-dihydroxycarbazole, 1.25 parts of 2,6-dibromophenol, and 0.24 parts of formaldehyde to 15 parts of N,N-dimethylformamide solvent, stir and disperse, heat to 60° C., react for 10 hours, and after the reaction is completed, add water to precipitate the product, filter it, wash it with methanol, and dry it to obtain intermediate 1;

[0025] (2) Intermediate 1, 1.05 parts of diphenyl carbonate and 0.005 parts of lithium acetylacetonate were subjected to transesterification reaction at normal pressure and 160° C. for 2 h under nitrogen protection, and then the pressure was reduced to 0.5 Torr and the temperature was raised to 250° C. for polycondensation reaction for 1 h. After the reaction was completed, heating was stopped, nitrogen was introduced to restore the system to normal pressure and cooled to room temperature to obtain a polycarbonate modified intermediate 2;

[0026] (3) Add 25 parts of epoxy resin to 75 parts of acetonitrile solvent, stir and disperse, then add polycarbonate modified intermediate 2, 0.2 parts of dibutyl terephthalate, and 0.1 parts of diaminocyclohexane, stir well, apply the mixture evenly on a glass sheet, and place it in an oven at 120°C for curing for 2 hours to obtain a modified epoxy resin conductive adhesive.

[0027] Embodiment 2:

[0028] A modified epoxy resin conductive adhesive comprises, by weight, 30 parts of epoxy resin, 1.55 parts of diphenyl carbonate, 0.36 parts of formaldehyde, 1.5 parts of 2,7-dihydroxycarbazole, 0.007 parts of lithium acetylacetonate, 1.8 parts of 2,4,6-tribromophenol, 0.3 parts of dioctyl isophthalate, 0.2 parts of diethylenetriamine, 15 parts of N,N-dimethylformamide solvent and 75 parts of acetonitrile solvent.

[0029] (1) Add 1.5 parts of 2,7-dihydroxycarbazole, 1.8 parts of 2,4,6-tribromophenol, and 0.36 parts of formaldehyde to 15 parts of N,N-dimethylformamide solvent, stir and disperse, heat to 80° C., react for 5 hours, and after the reaction is completed, add water to precipitate the product, filter it, wash it with methanol, and dry it to obtain intermediate 1;

[0030] (2) Intermediate 1, 1.55 parts of diphenyl carbonate and 0.007 parts of lithium acetylacetonate were subjected to transesterification reaction at normal pressure and 200° C. for 3 h under nitrogen protection, and then the pressure was reduced to 0.5 Torr and the temperature was raised to 270° C. for polycondensation reaction for 1.5 h. After the reaction was completed, heating was stopped, nitrogen was introduced to restore the system to normal pressure and cooled to room temperature to obtain a polycarbonate modified intermediate 2;

[0031] (3) Add 30 parts of epoxy resin to 75 parts of acetonitrile solvent, stir and disperse, then add polycarbonate modified intermediate 2, 0.3 parts of dioctyl isophthalate, and 0.2 parts of diethylenetriamine, stir well, apply the mixture evenly on a glass sheet, and place it in an oven at 120°C for curing for 2 hours to obtain a modified epoxy resin conductive adhesive.

[0032] Embodiment 3:

[0033] A modified epoxy resin conductive adhesive comprises, by weight, 35 parts of epoxy resin, 2.1 parts of diphenyl carbonate, 0.48 parts of formaldehyde, 2 parts of 2,7-dihydroxycarbazole, 0.01 parts of lithium acetylacetonate, 2.5 parts of 3,5-dibromophenol, 0.4 parts of dibutyl isophthalate, 0.3 parts of methylenebiscyclohexylamine, 15 parts of N,N-dimethylformamide solvent and 75 parts of acetonitrile solvent.

[0034] (1) Add 2 parts of 2,7-dihydroxycarbazole, 2.5 parts of 3,5-dibromophenol, and 0.48 parts of formaldehyde to 15 parts of N,N-dimethylformamide solvent, stir and disperse, heat to 80° C., react for 10 hours, and after the reaction is completed, add water to precipitate the product, filter it, wash it with methanol, and dry it to obtain intermediate 1;

[0035] (2) Intermediate 1, 2.1 parts of diphenyl carbonate and 0.01 parts of lithium acetylacetonate were subjected to transesterification reaction at normal pressure and 250° C. for 4 hours under nitrogen protection, and then the pressure was reduced to 0.1 Torr and the temperature was raised to 300° C. for polycondensation reaction for 2 hours. After the reaction was completed, heating was stopped, nitrogen was introduced to restore the system to normal pressure and cooled to room temperature to obtain a polycarbonate modified intermediate 2;

[0036] (3) Add 35 parts of epoxy resin to 75 parts of acetonitrile solvent, stir and disperse, then add polycarbonate modified intermediate 2, 0.4 parts of dibutyl isophthalate, and 0.3 parts of methylenebiscyclohexylamine, stir well, apply the mixture evenly on a glass sheet, and place it in an oven at 120°C for curing for 2 hours to obtain a modified epoxy resin conductive adhesive.

[0037] Comparative Example 1: The preparation method is basically the same as that of Example 1, except that the bromine-based reactive flame retardant is absent.

[0038] Comparative Example 2: The preparation method is basically the same as that of Example 1, except that 2-aminohydroquinone is used instead of 2,7-dihydroxycarbazole.

[0039] Comparative Example 3: The preparation method is basically the same as that of Example 1, except that the ester exchange melt polycondensation reaction in step (2) is skipped, and step (3) is directly performed using intermediate 1 instead of intermediate 2.

[0040] Conductive adhesive performance test: The modified epoxy resin conductive adhesive prepared in Examples 1-3 of the present invention and Comparative Examples 1-3 were tested for application performance under the same conditions: 5 grooves with a length, width and height of 50 mm, 10 mm and 5 mm were engraved in a glass plate, and the modified epoxy resin conductive adhesive was cured in the grooves. The resistance at both ends was measured using an intelligent low resistance tester, and then the volume resistivity was calculated, and finally the average value of the volume resistivity was calculated; the heat resistance of the conductive adhesive was tested using a thermogravimetric analyzer. Under nitrogen conditions, the heating rate was 10°C, the test temperature range was 40-550°C, and T 5％ It is the temperature at which the mass loss is 5%; an oxygen index tester is used to test the flame retardant properties of the material.

[0041] The comparative test results are shown in the following table:

[0042] Resistivity (Ω·cm) <![CDATA[T 5％ / ℃]]> Oxygen index / % Example 1 <![CDATA[3.13×10 -4 ]]> 381.7 25.2 Example 2 <![CDATA[3.05×10 -4 ]]> 389.2 27.6 Example 3 <![CDATA[2.82×10 -4 ]]> 403.5 31.2 Comparative Example 1 <![CDATA[2.97×10 -4 ]]> 391.1 16.3 Comparative Example 2 <![CDATA[6.44×10 -4 ]]> 397.2 25.8 Comparative Example 3 <![CDATA[3.48×10 -4 ]]> 316.4 26.9

[0043] As can be seen from the above table, compared with Comparative Example 1, Example 1 has a higher oxygen index, that is, better flame retardancy. This is because Comparative Example 1 does not contain brominated flame retardants, while the brominated flame retardants in Example 1 capture free radicals generated by combustion during combustion, and generate HBr gas to isolate the air, so that the combustion is slowed down or stopped, thereby improving the flame retardancy; compared with Comparative Example 2, Example 1 has a lower resistivity, that is, better conductivity. This is because the 2-aminohydroquinone in Comparative Example 2 has only one benzene ring and a limited range of electron migration, while the large π bond and p-π conjugated system of 2,7-dihydroxycarbazole in Example 1 are conducive to the migration of electrons, thereby greatly improving the conductivity of the conductive adhesive; compared with Comparative Example 3, Example 1 has a higher T 5％ , i.e., better heat resistance. This is because Comparative Example 3 skips step (2) and does not prepare the polycarbonate modified intermediate 2, while the polycarbonate modified intermediate 2 in Example 1 introduces more rigid structures, such as benzene rings, carbazole, and polycarbonate, which increases the molecular packing density of the material, thereby improving the heat resistance.

[0044] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A modified epoxy resin conductive adhesive, characterized in that: The raw materials are calculated by weight and include: 25-35 parts of epoxy resin, 1.05-2.1 parts of diphenyl carbonate, 0.24-0.48 parts of formaldehyde, 1-2 parts of conductive filler, 0.005-0.01 parts of catalyst, 1.25-2.5 parts of flame retardant, 0.2-0.4 parts of plasticizer, 0.1-0.3 parts of curing agent, 15 parts of N,N-dimethylformamide solvent and 75 parts of acetonitrile solvent.

2. The modified epoxy resin conductive adhesive according to claim 1, characterized in that: The conductive filler is 2,7-dihydroxycarbazole.

3. The modified epoxy resin conductive adhesive according to claim 1, characterized in that: The catalyst is lithium acetylacetonate.

4. The modified epoxy resin conductive adhesive according to claim 1, characterized in that: The flame retardant is a bromine-based reactive flame retardant.

5. The modified epoxy resin conductive adhesive according to claim 4, characterized in that: The bromine-based reactive flame retardant is one of 2,6-dibromophenol, 3,5-dibromophenol and 2,4,6-tribromophenol.

6. The modified epoxy resin conductive adhesive according to claim 1, characterized in that: The plasticizer is one of dibutyl isophthalate, dioctyl isophthalate, dibutyl terephthalate, dioctyl terephthalate, diethylene glycol benzoate, and propylene glycol sebacate.

7. The modified epoxy resin conductive adhesive according to claim 1, characterized in that: The curing agent is one of diaminocyclohexane, methylenebiscyclohexaneamine and diethylenetriamine.

8. The method for preparing the modified epoxy resin conductive adhesive according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) Adding a conductive filler, a flame retardant, and formaldehyde to an N,N-dimethylformamide solvent, stirring and dispersing, heating to 60-80° C., and reacting for 5-10 hours. After the reaction is completed, adding water to precipitate the product, filtering, washing with methanol, and drying to obtain an intermediate 1; (2) subjecting the intermediate 1, diphenyl carbonate and the catalyst to an ester exchange reaction at normal pressure and 160-250° C. for 2-4 hours under nitrogen protection, then reducing the pressure to 0.1-0.5 Torr and heating to 250-300° C. for polycondensation reaction for 1-2 hours. After the reaction is completed, heating is stopped, nitrogen is introduced to restore the system to normal pressure and the system is cooled to room temperature to obtain a polycarbonate modified intermediate 2; (3) Add epoxy resin to acetonitrile solvent, stir and disperse, then add polycarbonate modified intermediate 2, plasticizer, and curing agent, stir well, apply the mixture evenly on a glass sheet, place in an oven at 120° C. for curing for 2 h, and obtain a modified epoxy resin conductive adhesive.

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